THE CARBONIFEROUS SYSTEM—PERIOD OF GIGANTIC VEGETABLES.
The system of rocks termed the Carboniferous constitutes the most
remarkable, as well as the most valuable, group in the whole range of
geological investigation. The strata of which this system is composed,
evince design in the clearest and the most unequivocal manner, testifying
to the mandate given on the third day of Creation, that the earth
was to bring forth grass, the herb yielding seed, and the fruit-tree
yielding fruit after its kind; and which, in the prodigious development
of vegetable matter that so early and rapidly ensued, demonstrate such
productive powers of nature to have been chiefly prospective, and
preparatory to the still higher development of life that was to follow.
Milton has finely imagined a tradition in heaven, long subsisting,
concerning the creation of a new world, and of man for whose habitation
it was intended:
“Space may produce new worlds, whereof so rife,
There went a fame in heaven, that He ere long
Intended to create, and therein plant
A generation, whom his choice regard
Should favor equal to the sons of heaven;
The happy seat
Of some new race, called Man.”
The idea here so beautifully expressed is, that the cosmical arrangements
of the earth were, from the beginning, so conducted as to be subservient
to man’s well-being; and, certainly, nothing could show more the dignity
of the new race, or the interest taken in them by their Creator, than
this tradition which ran of them in other spheres. But geology, more
to be relied on than poetry, furnishes demonstrative evidence of the
anterior designs and purposes of Omnipotent Wisdom in actually fitting
up “the happy seat,” and in storing it beforehand with materials suited
to the wants and comfortable subsistence of him who was to be its
loftiest inhabitant. The coal-metals, in the discovery of their history
and position, alone vindicate the importance of geology as a science.
The whole group with which they are associated, in their mineral and
vegetable contents, their place in the system, and the means provided at
once for protection and excavation, manifest a series of contrivances so
expressive of design, as cannot fail, when read aright, to draw forth our
gratitude and wonder.
I. THE MINERAL INGREDIENTS, POSITION, AND ARRANGEMENT OF THE
CARBONIFEROUS SYSTEM.—The rocks belonging to this formation, in the order
of superposition, succeed the old red sandstone, consisting of a series
of deposits of great thickness, of an infinite number of alternations and
varieties, and nearly the same in every coal-field all over the earth.
They constitute one great group of marked physical characters, formed
under similar conditions, and produced during the same epoch or period of
time. The out-crop of the beds meets the eye along the ridge of which the
Lomonds may be taken as the center, ranging eastward by St. Andrews to
Fifeness Point, and extending indefinitely westward by Stirling, Campsie
Hills, Port-Glasgow, to the coast of Arran. The southern lip of the great
coal basin of Scotland stretches from the German Ocean, near Dunbar, to
the Ayrshire coast in the North Channel, flanked by the old red sandstone
and Silurian rocks almost continuously throughout. And within the space
now indicated are situated all the principal coal-fields of the northern
part of the empire.
The lower beds of the formation consist generally of coarse-grained
sandstone, termed by the English geologists millstone grit, and inclose
a few thin unworkable seams of coal. Bands of ironstone, shale, and
sandstone are superimposed in repeated alternations. A thick massive
limestone lines the edges, feathering in and out through the area
of the basin which contains the coal metals. This is the mountain
limestone, the most of which is supposed to have once existed as coral
reefs, raised on the bottom of shallow seas, so subdivided as to form
suitable compartments for receiving and retaining the matter of the coal.
Accordingly, corals, encrinites, and shells everywhere prevail in the
rocks of this deposit, and, in some instances, present the appearance
of a homogeneous, agglutinated mass of the remains of these marine
animals—the first of living creatures which the waters were charged to
bring forth, and with which they were now swarming. The bituminous beds,
the true coal, generally occupy a central position in the group, firmly
caked and inclosed between the arenaceous and shaly strata. The number
of seams vary in different basins, ranging in Scotland from eleven to
thirty-two or thirty-three, and comprising an average thickness of the
useful mineral of a hundred and twenty feet. The varieties of coal—as
anthracite or blind-coal, cannel or parrot, and the common house or
glance-coal—are occasioned chiefly by the different proportions of the
bituminous elements which enter into their composition. Compared with
Scotland, the coal-measures of England and Wales are of a greater average
thickness, lie far beneath the surface, and contain in general a greater
proportion of bitumen.
The basin containing the coals, as defined above, is inclosed within the
great chains of primary and secondary mountains of the central district
of Scotland, which were upheaved into dry land before the coal-measures
were formed. A period of violent disturbance had thus passed away, when
the carboniferous formation bears evident tokens of having been begun and
completed in tranquil waters. But after being collected, the coal-metals
were exposed to the action of disturbing forces: eruptive masses, of
igneous origin, have invaded their domain; basalts and greenstone,
trap dykes and veins, are everywhere found within their inclosure;
and apparently the utmost disorder and irregularity now reign, where
order and stillness once prevailed. But look a little closer: examine
the length and breadth of any coal-field in any part of the world, and
you will discern proofs of a purpose, not only in the quality of their
materials, but in the position, arrangement, and grouping of the metals;
those very disturbing forces, to which they and all earthly things have
been exposed, giving unequivocal testimony of an overruling intelligence
continuing, through all ages, to superintend and guide their various
operations.
Study any coal-field in your neighborhood, and observe _the place_ of
the mineral. It does not lie exposed upon the surface, but is placed at
a considerable depth in the earth; of which many are apt to complain,
thinking that, if a different arrangement had prevailed, much needless
labor and expense would have been saved. But the constituent elements
of coal are such, that by exposure on the surface the mineral would,
in a comparatively short period of time, have run to waste and decay.
Even a thick covering of earthy mold would not have been sufficient to
protect it; and therefore was the treasure purposely hid in the earth,
and so inclosed that the floods could not wash it away. Then consider the
_quality_ of the rocks by which the coal is protected, and along with
which it is invariably associated. These consist of limestone, sandstone,
shale, and clay ironstone, which always occupy the same basins, and
alternate with the coal sometimes in a series of more than a hundred
beds. Such a group of well-characterized rocks not only act as a guide
for determining the localities of the valuable mineral, but they serve
the double purpose of facilitating the excavation, by affording at once
a safe roofing to the mine, and an easy passage for the drainage of
the water which accumulates in the pits. No other class of rocks would
have been so suitable. The granite and crystalline rocks would have
been inconvenient, or wholly unfit: no borings could have been effected
through such materials to any extent; the operations underneath would
have been equally difficult and unmanageable; and through such hard
compact substances the drainage must have been impracticable. But a still
more remarkable indication of contrivance arises from _the elevated_
and _inclined position_ into which the coal strata have been thrown.
Had they remained in the position which they originally occupied, and
been covered with the vast accumulations which have subsequently taken
place, their depth would have been utterly beyond the industry of man to
have reached. Hence the waters have disappeared, having accomplished the
purpose for which they were, in this instance, spread over the earth, and
the rocks formed beneath them have lifted up their heads; not uniformly,
or in one continuous unbroken mass, but divided into small sections, and
inclined in every possible direction. The wisdom of this appears from
two considerations: From their inclined position, the various beds of
coal are worked with greater facility than if they had been horizontal, a
_level_ is produced for the drainage of the water, and the edges of the
coal bent upward are brought nearer the surface. But these advantages
are, every one of them, increased incalculably by the division of the
coal-field into limited sections, whereby less water is allowed to
accumulate than if the beds had been indefinitely extended; their lower
extremities are prevented from being plunged to a depth that would be
inaccessible; and their several portions arranged in a series of tables,
like the steps of a stair, rising one behind another, and gradually
inclining outward from the lower to the upper seams of the basin. Again,
every coal-field is furnished with a system of checks, in the shape of
_faults_ or _dykes_, against floodings, fire-blaze, and other accidents
that occur in the operations of mining. These faults or dykes consist of
clay, the detritus of the associated rocks, or of intruded whinstone,
with which the fractures produced at the period of the disruption and
elevation of the coal-field have been filled up, and the various sections
of the metal insulated, and contracted to more workable dimensions.
They present the appearance of a vertical wall, cutting the strata at
right angles; and, though often occasioning much inconvenience and
interruption, yet, as every experienced collier well knows, forming
upon the whole his greatest safeguard, and essential every way to his
operations. To all which add, as _constants_ in every coal-field, the
minerals of lime and iron, gifts, both of them, of inestimable value:
the former in the amelioration of the soil and construction of every
social edifice; the latter ductile and plastic as wax, capable of being
welded, and yet, by a slight chemical change, possessed of adamantine
hardness; and the coal always there, in juxta-position, to serve as a
fuel for the reduction of the limestone and ironstone into their economic
properties—properties starting into agency as if by a miracle.
These are a few of the facts connected with the arrangement and
distribution of the coal-measures, in whatever quarter of the globe
they are found. Is it possible to resist the conclusion, that, in such a
disposition of things, there are the clearest indications of contrivance
and design? Nay, that the argument derived from the construction and
positions of the solid parts of the earth is the same in kind, if not in
degree, with that which is so irresistibly demonstrative in the case of
the organic structure of the living frame? The dance of atoms imagined
by the philosopher of antiquity, could never have terminated in the
perfect order and harmony of the heavenly bodies—innumerable systems of
worlds maintained,—each hung upon nothing, and duly preserved all of them
in their respective spheres. Equally impossible is it to contemplate
a disposition of things so adapted, and indeed so indispensable, for
availing ourselves of the mineral treasures of the earth—essential
to our wants, and ministering so directly to our social comfort and
improvement—and yet to refer the whole, or any part, to the blind
operation of fortuitous causes. Impossible, indeed, it ever will be,
for the human mind to embrace or unravel all the mysteries of creation;
but thus admitted to the mighty wonders of the interior, we are almost
enabled to trace the history of the moving atoms from their chaotic
disorder into their places and arrangement in the visible universe—to
see dead matter assuming the forms of life and organization—clothing the
earth for a season with luxuriance and beauty—buried for ages under the
solid rock—and again, out of coldness and death, affording light, and
warmth, and power to the successive generations of men.
II. ORIGIN OF THE CARBONIFEROUS ROCKS.—The strata comprised within the
coal-measures are variously estimated; being, in some instances, about
eleven thousand feet in thickness; in other cases, of much greater depth;
and of this mass of matter, the coal itself does not occupy more than
a maximum average of one hundred and fifty feet. The shales consist of
thin beds of mud, washed down by the rivers from the neighboring heights,
and would appear to have formed the soil on which subsisted a rank
vegetation; the impressions of plants, roots, and trunks of trees being
still found in a standing position. It is from these bands of mudstone
that the best specimens of the flora of the period are derived; every
thin splitting presenting the most entire and beautifully-preserved
figures of fronds and stems. The ironstone is usually mixed up or
associated with the shales, and consists, like them, of comparatively
thin beds of ferruginous clay. The sandstones, of which the greater
proportion of the mass consists, have clearly resulted in the continued
action of the same causes that produced the old red deposit of the
anterior period. But the two remarkable products of the age are the
calcareous and coaly strata, which give character to the system as
well as the epoch in which they were formed; the one showing a sudden
development of carbonate of lime, and the other an increase of vegetable
matter, whose enduring monuments point them out as the most striking
cotemporaneous and co-extensive formations on the surface of the globe,
or connected with the history of our planet. The bituminous products of
the Silurian period, if the anachronism may be pardoned, are but as the
gleanings after the full harvest.
The limestone is unquestionably of marine origin, as the countless
myriads of testacea inclosed in it testify, and was probably constructed
by the primeval families of those island-making architects by which the
coral-reefs of our present seas are raised, and whose instincts have
found them similar employment in all ages of the world. The limestones of
the earlier systems may have been formed in the same manner; and then, as
in the subsequent period, we must go to the great original storehouse of
Nature for the materials on which they worked. The spoils of the primary
rocks could not supply them, as the quantity of the carbonate of lime
therein contained bears no proportion to the masses which constitute
the mountain limestone group. But the calcareous substance was already,
in some elementary form, in combination or otherwise, in existence—the
animals capable of secreting and arranging it anew, as the secondary
instruments of creation, were abounding in the seas—shallow bottoms over
the subjacent sandstones of the devonian system, and within the required
conditions of life, were prepared for their operations. The waters had
now brought forth abundantly the moving creatures, which, at first more
scantily distributed, produced the limestone of the silurian rocks, as
the arborial remains of the land, in like stinted measure, are inclosed
in the older palæozoic deposits. Their day of increase as it advanced,
each after their kind, is recorded in the vast accumulations of animal
and vegetable matter which compose the strata of the carboniferous
system, both of an order and quality purposely so arranged, and never
upon the same scale of magnitude to be repeated in the combustible
mineral.
This account, as given by geologists, of the origin of the mountain
limestone, is rendered not only probable, but almost certain, by the
manner in which we find these little insects, the coral-builders,
constructing their piles of masonry at the present day. For example,
certain species of polyps, of solitary habits, work alone, each rearing
a single stem or stalk, from which others project; then more stems are
produced, until, upon the completion of the whole, there results one of
those beautiful arborescent structures so much prized as ornaments for
cabinets and drawing-rooms. Some, again, attach themselves to the loose
stones, upon which they form their little tree or flower-top; others
adhere to the solid rock, from which there springs a stony vegetation,
rivaling often, in variety, luxuriance, and brilliancy, the most showy
vegetable productions of tropical climes. But a certain class are
gregarious, and will only work in company. Myriads of these inhabit the
Pacific, constructing entire islands, and throwing up mighty barriers of
rock, and threading over vast areas of the sea with inosculating lines
of coral reef. The calcareous accumulation, known as the Great Barrier
Reef, extends for about a thousand miles in length, by about thirty in
mean breadth, filling up, with its various reticulations, the whole
intermediate space betwixt the coast of Australia and Bristow Island, off
the coast of New Guinea. The works of these minute creatures thus occupy
an area which may be roughly estimated at thirty thousand square miles;
the different branches forming compartments of variable extent, which are
divided into linear, outer, and inner reefs, and embracing within their
ample folds the entire spoils of ocean living or floating in these parts.
The mountain limestone of our own country, formed in like manner on the
sea-bottom of corallines, has a wide geographical range, extending from
the bay of St. Andrew’s on the north, to the extremity of Wales on the
south; passing into Ireland, where it is elevated into long ridges, or
occupies the mountain-slopes; and forming outliers or extended barriers
in all the southern counties of Scotland, and in the greater portion of
the northern, the middle, and the south-western districts of England.
These were the coral reefs of an ocean now raised into dry land, divided,
too, into outer and inner compartments, or arranged into systems of lines
and branches, which diverged from or inosculated with each other. Nor
does the resemblance between the recent and the more ancient formations
stop here, but extends to the structure of the deposits, lithologically
considered, the mechanical, sub-crystalline, and crystalline texture
being exhibited in both sets of rocks. Thus, in the examination of Heron
Island, the coral beds, one to two feet thick, are found to have a
tendency to split into slabs, and joints are observed to cross each other
at right angles, parallel to the dip and strike, respectively, giving to
the still living coral rock the jointings, cleavage, and stratification
of the greater palæozoic deposits. Naturalists divide these polyps
into existing and extinct races. But whether extinct and specifically
different, or otherwise, they are creatures of a family, possessed of the
same habits and performing the same operations, now as of old; and if,
as geologists say, millions of ages have elapsed between the actings of
the first and last generations, our admiration will be only all the more
unbounded by thus witnessing the harmony of creation through indefinite
time, and the accuracy of the Book which contains the record of it.
The coal itself, as now universally admitted, is of vegetable origin.
Under the microscope, in the most compact specimens, the tissues by which
all the coal plants are more or less distinguished can be distinctly
traced. Chemically considered, its vegetable origin is equally well
established. Carbon constitutes the principal ingredient of the mineral
the quality of which enters most abundantly into the composition of
vegetables. One theory of its formation is, that vegetable matter,
carried to the sea or extensive lakes, has undergone a process of
decomposition, by which, while some of its principles may have escaped
or been evolved in new combinations, the carbon, with a portion of the
hydrogen, has remained; this, mixed with more or less earthy matter, has
in its soft state been consolidated by the force of aggregation simply,
or by compression from the superincumbent strata, and the action of a
higher degree of temperature than now exists. Others are of opinion
that coal is the altered residuum of trees and smaller plants that have
grown on the spot where we now find them—that the forests were submerged
and covered by detrital matter, which was upraised to form a foundation
and a soil for another forest, to be in its turn submerged and converted
into coal—and that thus the alternations which the vertical section of
a coal-field exhibits are to be accounted for. The former views are
maintained by Sir R. Murchison and other eminent geologists. The latter
have been adopted by Sir Charles Lyell, in consequence mainly of the
arrangements and structure observed in the remarkable coal-field of Nova
Scotia, where he states that there is a range of perpendicular cliffs
in the Bay of Fundy, composed of regular coal-measures, inclined at an
angle between twenty-four and thirty degrees, whose united thickness
is between four and five miles. By neither theory, perhaps, nor by any
other yet advanced, is it possible to reconcile all the appearances which
that singular compound, a COAL-FIELD exhibits—the various changes which
the vegetable matter has undergone to convert it into lignite, jet,
common coal, cannel coal, and anthracite, two or more of these varieties
often occurring in the same coal-measures—in one quarter the clearest
indications that the sea has let in its floods and mingled its spoils
with those of the land, and in another quarter, through fourteen thousand
feet, for example, of the drift accumulations in Nova Scotia, that
there is not a trace even of any substance of a _marine_ character, all
appearing to have been deposited in fresh water. But while no explanation
yet given of the phenomena can be regarded as satisfactory, while Nature
withholds much, and ever will, of the wonderful processes through which
she attains her ends, the vegetable source of the product cannot be
questioned; nay, the origin of coal from the extinct forests, from the
trees and plants of a former age, is so very probable, that some beds
sound like wood under the beat of the hammer; and large areas, when thin
slices are placed under the microscope, are found in every portion to
retain the woody-fibrous structure.
III. THE BOTANICAL CHARACTERS of the flora of the coal period form of
themselves an interesting subject of study, and suggest some very
important considerations as to the history and purpose of the formation.
These will be best understood by a reference to the structure and habits
of plants in general. Those of the coal, it will thence be seen, belong
exclusively to one or two families,—as ferns, palms, and coniferæ,—which
seem to have grown in every soil, and to have been adapted to every
climate.
The most general divisions of existing plants are into the _vasculares_
and _cellulares_. The former kinds all bear flowers, possess a system
of spiral vessels, and are termed phonogamous. The latter, on the other
hand, are flowerless, have no spiral vessels, and are denominated
cryptogamous.
Another extensive subdivision of plants proceeds upon their anatomical
structure, and the laws which regulate their mode of growth. Thus one
class, it has been observed, increase in bulk by additional increments
to the outside of all the parts which compose the plant, as the roots,
stems, and branches; another, by additions to the inside of all these
members: and for this reason the former are called exogenous, and
the latter endogenous. In the one case the new or youngest growth is
always exterior to the old; and if thus left unprotected, it will be
readily admitted that the growth of all such plants would be greatly
and constantly endangered by atmospheric as well as innumerable other
causes. The remedy provided by nature against this, is a covering of the
substance called bark, which is folded round the entire exterior, stem
and branches, of the whole exogens, and within which the newly-formed
tissue is all safely deposited. No plant, on the other hand, whose growth
is from within, needs any such protection, and accordingly none of
them—as all the grasses, corns, canes, and fungi—are possessed of bark,
or any analogous membrane. The bark is an ephemeral substance, which
lasts only for a year, and has annually to be renewed.
The additions to all exogenous plants are indicated in the stem or
trunk, by concentric lines or circles. In the center there is a cellular
substance called pith. When you take, therefore, a cross section of the
trunk of this class, the structure and parts will be arranged thus—bark
on the outside, pith in the center, and between these, concentric
deposits of woody matter, and all connected into a solid mass by plates
of comb-like tissue, radiating from the interior to the circumference,
and termed medullary rays. A structure like this, so closely and firmly
united, and filled up through all its parts, was surely intended for
endurance; and yet out of this class of the vegetable tribes, nature has
selected few of her carboniferous models. The plants of the period, as
yet detected, are composed chiefly of cellular tissue, mixed up with the
substance of the stem, and without pith, medullary rays, concentric woody
deposits, or the binding ligament of bark. The hardy oak and tall slender
cane may be taken as examples of the two modes of structure—the former
allied to existing, the latter to extinct families.
Another ground of distinction among plants consists in the leaves
or flattened expansions, from which they derive all their grace and
symmetry. This is farther connected with the seed and rudimentary organs,
and gives rise to the division into _cotyledonous_ and _acotyledonous_
plants. The non-flowering or cryptogamous are all of the latter kind. The
flowering or phonogamous not only belong to the former, but are again
subdivided into monocotyledonous or dicotyledonous, according as their
seed-vessels are possessed of one or of two lobes. Where there are two
lobes the expansion of the germ upon bursting from the ground terminates
in two imperfect leaves, by which the botanist can at once determine the
class to which it belongs. The corns and grasses have single cotyledons,
from one extremity of which descend the roots, and from the other the
stem springs up, terminated with a single leaf.
The leaves perform important functions in all those orders of plants
with which they are connected, and serve as interesting guides in fossil
botany, which seldom derives any assistance from the more destructible
and “fleeting flower.” The leaves of plants consist of a complicated
net-work of vessels, filled up in the interstices by cellular tissue,
and covered over with a thin epidermis or skin. Those belonging to the
monocotyledonous sub-class are traversed by a number of parallel veins,
while dicotyledonous leaves are divided into regular compartments,
some of which upon withering display the most perfect and beautiful
system of reticulation, rivaling in delicacy of texture the wing of
the gossamer. Leaves which outlast the season, as in evergreens, are
termed non-deciduous, and are covered or interwoven with a thin crust
of silex, which at once serves to protect and communicate to these
ornamental shrubs their bright enameled appearance. The grasses possess
this property, and some of them can elaborate in their joints crystals of
considerable magnitude. The leaves of ferns are called fronds, and differ
from true leaves in bearing the reproductive organs on the surface, while
the slightest inspection of their form and mode of expansion readily
distinguishes them from all others. Fronds, properly so termed, originate
in the stem and are part of it; there is no distinct line of demarkation
between them: stem, leaf, and spori, or seed; are all as one body; and
thus, as being of one piece, these membranous organs have been quaintly
likened to a garment without a seam.
From this brief description it will be seen that all plants and trees
arrange themselves under two great classes, namely, the soft and spongy,
or the hard and fibrous-woody structure. The remains of such as have been
detected in the carboniferous rocks belong almost exclusively to the
former class, the cryptogamiæ and endogenæ, while of the three hundred
and upward of fossil species which have been described and figured, not
more than ten, and some of these still of doubtful characters, can be
regarded as of exogenous and true woody growth. Ferns, mosses, palms,
and gigantic succulent plants, now all allied to those of tropical
climates, constitute the vast preponderancy of the fossil flora of the
age in question. Are we to infer from this that the other families and
tribes which at present so abundantly cover the earth were not then in
existence? The botanist can now refer to his catalogue of eighty to a
hundred thousand species of existing plants, growing in the different
regions of the globe, and of widely distinguished habits and forms;
and were few or none of these in being then? We possess not, as yet,
sufficient data for the solution of this very interesting problem,
although in the progress of geological discovery, every year is adding to
the list, and giving us a more extended acquaintance with the vegetable
products of the coal period. An important experiment recently made by
Professor Lindley would seem to favor the probability that a far more
numerically abundant flora had then existed. One hundred and seventy
plants were thrown into a vessel containing fresh water, and among them
were species belonging to all the natural orders of which the flora of
the coal-measures consists, and also to other natural orders which it
might have been expected would be found associated with them. In the
course of two years, one hundred and twenty-one species had disappeared,
being entirely decomposed, and of the fifty which remained, the most
perfect specimens were those of coniferous plants, ferns, palms,
lycopodiaceæ, and the like—the families, all of them, most allied to
those preserved in the coal-measures.
Now the important fact to be attended to in this experiment is, the wide
geographical distribution during the carboniferous era of those tribes
of plants which enter most certainly and abundantly into the composition
of the coal metals. Many others may, and doubtless did, flourish within
the period of the formation. But that the plants, possessed of the most
conservative vegetable qualities, and the most capable of resisting
solution in water, should be precisely the kinds which had then a
universal range over the earth’s surface, can be ascribed to nothing else
than to a wise predetermined purpose and arrangement. These plants were
growing in every region. Every clime favored them—every soil nourished
them. The bituminous product was intended for man’s use, whose family
was destined to inhabit the whole earth. How irresistible the conclusion,
corroborative of all the proofs of design derived from the nature
and structure of the coal-measures, that, anticipating his wants and
providing for his improvement, nature purposely constructed such forms of
vegetable life, possessed, like the watch, with a compensation balance
so as to suit every condition, and to thrive in every land; or, what
is equally probable and consonant to the requirements of the problem,
that there was such a uniformity of climate and temperature, and other
chemical adjustments, as were most adapted to the peculiar and prevailing
vegetation of the period.
IV. THE ORGANIC REMAINS we proceed to consider more in detail, where a
remarkable contrast will be observed between the vegetable and animal
types presented, so far as they have been respectively fossilized and
preserved. The vegetables are nearly all of terrestrial, the animals are
as generally and predominantly of marine, characters. Is this the result
of blind chance, or of contrivance and foresight?
The plants of the coal epoch consist chiefly of the cryptogamia, and
of these the ferns are the most abundant, composing, according to the
estimate of M. Brongniart, about two-thirds of the entire carboniferous
flora.
[Illustration: 1. Sphenopteris linearis; 2. Pecopteris Mantelli; 3.
Sphenopteris affinis.]
The number of known existing ferns amounts to between seven and eight
hundred, of which about fifty species belong to Great Britain, and
upward of two hundred to the inter-tropical island of Jamaica. Nearly
two hundred fossil species have been discovered in the British coal
strata alone. The fossil genera most common to the district around, and
occurring in every section of the great valley of the Scottish lowlands,
are cyclopteris, neuropteris, pecopteris, and sphenopteris. The shales
and clay-ironstones in which these beautiful plants are detected, are
generally of a dark brownish color, while the impressions are all of
the deepest jet, bringing out in lively contrast the complete cast
of the fronds. There is a great resemblance between the specimens of
extinct ferns and the existing families of our filices, now growing
on every hill, brae, or mountain corrie; and, if this were all the
difference, nature would seem to have departed but little from her
original models. But the presumption is that most, if not all, the
ferns of the coal era were trees which attained to a great height, and
similar to the tree-ferns now growing so abundantly in the islands of
the Pacific. The decorticated stems and trunks are deeply indented with
scars, the markings, it is supposed, of the fronds which dropped from
their feathery sides. This inference is borne out by the additional
circumstance, that the fossils are generally much flattened and
compressed, as would necessarily happen to succulent plants and such
trees as consisted of the cellular tissue of the endogenous class. What
a striking change in the vegetation of our country, where purple heaths,
and cheerful grasses, and luxuriant corns, and forests of every tint
and structure, have replaced the long green stems, and dark somber hues
of the fern-clad regions of the olden times! The remains of this tribe
are so numerous as to have stinted, one would suppose, or utterly to
have prevented the growth and increase of every other order of plants,
bringing before the imagination the scenes of our Australian colonies,
so wild and wondrous to European eyes—and carrying back the mind to the
vision of primeval ages, through a long succession of times and their
events, the vista of an infant world.
The lycopodia, or club-moss tribe, are also very widely distributed
among the coal-measures, and attained in the earlier ages of the earth’s
history an equally gigantic size with the tree-ferns. At the present
day, they are all weak, prostrate plants, of from two to three feet in
length, and, following the same laws as the mosses and ferns, they are
most abundant in hot, humid situations within the tropics, and especially
in the smaller islands. As respects their botanical affinities, the
lycopodiums are intermediate between ferns and coniferæ on the one
hand, and ferns and mosses on the other; related to the first of those
families in the abundance of annular ducts contained in their axis, and
to the second in the whole aspect and outline of the stem of the larger
kinds. Indeed, so great is the resemblance between lycopodia and certain
coniferæ, that there is no other external character, except size, by
which they can be distinguished; and, according to Professor Lindley,
it is, at least, as probable that some of those specimens detected in
the ancient flora of the world, which have been considered gigantic
club-mosses, are really and truly pines, as that they are flowerless
plants.
Another family of fossil plants abundant in the coal formation are the
calamites, so named from their jointed reed-like structure. They attained
to the size of trees, trunks upward of a foot in diameter being often
met with, but still of such a soft succulent texture as to maintain the
character of being, if reeds, easily shaken by the winds. These, and
various specimens of the palm tribe, are to be found in every coal-field,
and often in such vast masses as to show that they constituted no
inconsiderable proportion of the flora of the period. Palms now only
flourish within the regions of the tropics, where, from their various
properties, as well as great productiveness as fruit-bearers, they
constitute the chief source of dependence to the inhabitants for all
their supplies of the necessaries, luxuries, and medicines of life. A
single spathe of the date contains about 12,000 male flowers: another
species has been computed to have 207,000 in a spathe, or 600,000 upon a
single individual. The spathe constitutes the raceme or flower-stem of
the tree, and on a single raceme of a Seje palm, Humboldt estimated the
flowers at forty-four thousand, and the fruits at eight thousand. When
these magnificent productions of nature covered the plains and marshes of
our northern climes, there were no roaming tribes to gather their fruits,
inhale their fragrance, or bask in their shades. And yet they were not
formed in vain. Buried in the rocks, their collected remains now yield
a product as useful and valuable to the human family—as contributive
to intellectual improvement, as they would have been to mere animal
enjoyment.
The genus sigillaria, one of the most common of the coal plants,
possessed the singular properties of being apparently hollow in the
center, yet with an inner woody axis floating in a woody succulent jelly,
and inclosed in a thick outer coating of bark. The trunk is beautifully
fluted with longitudinal parallel lines, regularly arranged along the
surface, and dotted all over with small scars, as if impressed by the
leaves penetrating through the bark into the central woody axis. The
stigmariæ, once supposed to be a distinct genus, are now generally
regarded as simply the roots of the sigillariæ; they are, for the most
part, found resting in their natural position, in large clusters often;
and forming with their dense matted fibers a floor of considerable
thickness, on which, season after season, the leaves fell as the coaly
matter accumulated. This tree grew to an enormous size, specimens of
four feet in diameter by fifty feet in length being frequently met with;
traces of a vascular and fibrous structure can be observed in the
stems—also the annular wood layers are sometimes beautifully defined;
and, combined with a coating of bark of an inch in thickness, the
probability is, that the sigillaria belonged to the exogenous class of
vegetables.
[Illustration: Calamite.]
But of all the plants found in the coal-measures, the CONIFERÆ or pine
tribe, distinguished by their punctated woody tissue, are the most
interesting, whether we consider their characteristic properties,
extensive distribution, antiquity, and consistency of habit through
all the epochs and changes of creation. Unlike the tree-forms already
noticed, the pines grow now as they grew before, inhabiting the same
places, and preserving the same appearances in bulk and figure. In
structure the coniferæ occupy a place intermediate between cellurares
and vasculares, connected with the former through the lycopodiums, and
with the latter by the myriceæ, or aromatic gale tribe. The scales of the
cones are regarded by botanists as true foliage or reduced leaves, and in
this respect they approximate to the genus zamia, of the order cycadeæ,
where these organs are distinctly developed as carpellary leaves. Thus
widely connected through the chain of vegetable life, the fossil pines,
discovered in our coal-fields, form also the most interesting link
between the present and the remote past, showing similar conditions of
vegetable existence and forest landscape. No class of plants have been
more useful to man than the whole pine family; none are more universal
in their distribution over the face of the globe; none are possessed
of such powers of endurance, existing through all time, and natives of
every part of the world, from the perpetual snows of Arctic America,
to the hottest regions of the Indian Archipelago. These trees differ as
remarkably in form as in size, ranging through every gradation from the
stinted juniper of the Grampians to the stately cedars of Lebanon. And
the fossil specimens, huge in dimensions as those of Craigleith are, do
not excel the existing races. The araucaria, or Norfolk Island pine,
attains a height of two hundred feet; and in the Oregon territory of
North-West America, there are species of the fir tribe (P. Lambertiana
and P. Douglasii), which rise to even still more gigantic proportions.
Figuratively, it is said of the cedar, that its branches shall cover the
earth, and in the shadow thereof all fowl of every wing shall dwell:
literally and truly we find, that members of the same family have existed
in all lands, and flourished in the mountains through all ages.
Compared with the present condition of things, New Zealand bears the most
striking resemblance in the character of its vegetation to the flora
of the ancient carboniferous age. “The number of species of plants at
present known is 632, of which 314 are dicotyledonous, and the rest, or
318, are monocotyledonous and cellular. The number of monocotyledonous
is very small in comparison with the cellular; there are 76 species.
The grasses have given way to ferns, for the ferns and fern-like plants
are the most numerous in New Zealand, and cover immense districts.
They replace the _gramineæ_ or grasses of other countries, and give a
character to all the open land of the hills and plains. Some of the
arborescent species grow to thirty feet and more in height, and the
variety and elegance of their forms, from the minutest species to the
giants of their kind, are most remarkable.”[4]
These few types of the flora of the ancient world clearly indicate the
course and progress of creation. A dense vegetable covering already
existed over all the earth. No grasses, indeed, as yet are found to have
clothed the plains. But marsh plants grew luxuriantly in the waters.
Fucoids and algæ abounded in the seas. The hills and mountains raised
high in air their pines, palms, and fern-trees; nor would creepers and
parasites be wanting, climbing to their topmost branches and mingling
their bright enlivening hues with the dark somber shades of the forest.
Earth heard the voice of its Maker, and everything good and seasonable
sprang from its teeming bosom.
The carboniferous limestones are everywhere loaded with ANIMAL remains.
Every member of the series, the ironstones, sandstones, shales, and
even the coal itself, all abound in relics of the past; and, as was to
be expected, the fossils chiefly belong to marine forms of life. And in
these there is no great departure, as might likewise be inferred, from
the orders, and even generic types, we have been surveying in the lower
formations. But there is an increase in the species of some of them, as
well as the introduction of new and distinct creations altogether.
[Illustration: 1. Product. scabriculus; 2. Inoceramus vetustus; 3.
Bellerophon tangentialis.]
Thus the corals and encrinites remain with scarcely a change in
outward form, but of increasing variety, and in countless myriads. The
trilobites are nearly extinct, while the annelidæ, which appear not in
the devonian system, return to the stage in greater numbers and diversity
of structure. The conchiferæ are likewise enlarged in every order; as
also the crustaceæ, which are more than quadrupled. Pteropodæ present
four genera in the silurian group, decline to one in the devonian,
which genus is not found in the carboniferous, but a new one takes its
place. The brachiopodæ are again very abundant, as they were in the two
former groups. The most characteristic shells of the order and period
are the productus, spirifer, terebratula. One genus of heteropoda,
the bellerophon, appeared in the silurian rocks, of which there were
eleven species. Eight species occur in the devonian system along with a
new genus, porcellia. The bellerophon numbers nineteen species in the
carboniferous rocks, and the porcellia, which occurs also, contains
three.
The cephalopods, the most predaceous of their kind, lose generically,
while they multiply prodigiously in species during the latter epoch. Thus
the goniatites alone amount to fifty-four, the nautili to forty-two, and
the orthoceratites, which had declined to twelve in the devonian, swell
to thirty-two species in the carboniferous series.
But the fishes in this group of rocks exhibit, unquestionably, the
largest amount, both in number and form, of new types. Here the sharks
and sauroids appear, for the first time, not small, or attenuated in
bulk, but vigorous, robust specimens of their kind, strong and expert
swimmers, armed with enlarged destructive organs, and every way equipped
for maintaining the due proportion of numbers, and the free trade
of the ocean. Thus of the order of placoids, there are twenty-eight
genera, and ninety-four species; of ganoids there are five genera, and
twelve species; and sauroids enumerate thirteen genera, and twenty-four
distinct and entirely new specific creations. A specimen of reptilian
life has here also been detected; and what is of still greater theoretic
importance, in tracing the course of creation, the immediately overlying
sandstones have yielded up impressions of the winged tribes that “fly in
the open firmament of heaven.” This interesting fact will, in its proper
place in the order of superposition, be more fully alluded to.
The genus holoptychius, which began in the old red sandstone, again
occurs in the carboniferous system, under eight new specific forms. Along
with the megalichthys, afterward noticed, these constitute the two great
natural families of fishes of carnivorous propensities, which give a
marked character to the period. The prodigious increase of the shark-like
creatures, of which not less than sixty species have been described from
thousands of teeth, fins, detached vertebræ, and other fragments, is
equally striking. Thus, in all, the faunæ of the carboniferous period
amount to upward of a thousand species, which have been either figured or
described.
In contemplating the period of creation under review, we are struck
not more with the forms of life which actually existed, than with the
absence of races which were afterward so abundant. No quadruped or true
terrestrial animal is found so low in the series of rocks, or mixed up
in any way with all this profusion of marine exuviæ. Fossil insects
and indications of other winged tribes have been detected; but no bone
nor foot-print of beast, or inhabitant of land, has anywhere been
discovered. The fact is all-important, as showing not only a plan, but a
progress and succession in the work of creation. A vegetation, so rank
and luxuriant as has been traced, trees towering hundreds of feet into
the sky, and branches of the densest foliage stretching on every side,
was amply fitted to afford shelter and food to families of terrestrial
creatures of every kind. But in the circumstance, that during this period
there were repeated alternations of marine and fresh water deposits,
and consequently repeated submergence and elevation of land, we see a
reason why the terrestrial races were not yet called into being. Great
continents, comparatively speaking, did not exist; and there was no
ark of safety provided to float them over the billows. Race after race
would have violently perished during every shift or subsidence of the
sea bottom: and hence, until the carboniferous series was completed and
a statical equilibrium established between the land and waters, few or
none of the races which afterward swarmed in our plains and forests were
introduced upon the scene.
[Illustration: Fragment of Encrinital Limestone.]