only because I wished to limit my sketch and to attempt, at least,
to give it the vividness of a special locality, but also because a
single such shore will give us as good an idea of the characteristic
fauna of the time as if we drew our material from a wider range.
There are, however, a great number of parallel ridges belonging to
the _Silurian_ and _Devonian_ periods running from east to west,
not only through the State of New York, but far beyond, through the
States of Michigan and Wisconsin into Minnesota; one may follow nine
or ten such successive shores in unbroken lines from the neighborhood
of Lake Champlain to the Far West.
Although the early geological periods are more legible in North
America, because they are exposed over such extensive tracts of land,
yet they have been studied in many parts of the globe. In Norway, in
Germany, in France, in Russia, in Siberia, in Kamtchatka, in parts of
South America, in short, wherever the civilization of the white race
has extended, _Silurian_ deposits have been observed, and everywhere
they bear the same testimony to a profuse and varied creation. The
earth was teeming then with life as now, and in whatever corner of
its surface the geologist finds the old strata, they hold a dead
fauna as numerous as that which lives and moves above it. Nor do we
find that there was any gradual increase or decrease of any organic
forms at the beginning or close of the successive periods.
I think the impression that the faunæ of the early geological periods
were more scanty than those of later times arises partly from the
fact that the present creation is made a standard of comparison for
all preceding creations. Of course, the collection of living types
in any museum must be more numerous than those of fossil forms, for
the simple reason that almost the whole of the present surface of
the earth, with the animals and plants inhabiting it, is known to
us, whereas the deposits of the _Silurian_ and _Devonian_ periods
are exposed to view only over comparatively limited tracts and in
disconnected regions. But let us compare a given extent of _Silurian_
or _Devonian_ seashore with an equal extent of seashore belonging
to our own time, and we shall soon be convinced that the one is as
populous as the other. On the New England Coast there are about one
hundred and fifty different kinds of fishes; in the Gulf of Mexico
two hundred and fifty; in the Red Sea about the same. We may allow
in present times an average of two hundred or two hundred and fifty
different kinds of fishes to an extent of ocean covering about four
hundred miles. Now, I have made a special study of the _Devonian_
rocks of Northern Europe, in the Baltic, and along the shore of the
German Ocean. I have found in those deposits alone one hundred and
ten kinds of fossil fishes. To judge of the total number of species
belonging to those early ages by the number known to exist now is
about as reasonable as to infer that because Aristotle, familiar only
with the waters of Greece, recorded less than three hundred kinds
of fishes in his limited fishing-ground, therefore these were all
the fishes then living. The fishing-ground of the geologist in the
_Silurian_ and _Devonian_ periods is even more circumscribed than
his, and belongs, besides, not to a living but to a dead world, far
more difficult to decipher.
Extinct animals exist all over the world; heaped together under the
snows of Siberia, lying thick beneath the Indian soil, found wherever
English settlers till the ground or work the mines in Australia,
figured in the old encyclopedias of China, where the Chinese
philosophers have drawn them with the accuracy of their nation, built
into the most beautiful temples of classic lands--for even the stones
of the Parthenon are full of the fragments of these old fossils, and
if any chance had directed the attention of Aristotle toward them,
the science of Paleontology would not have waited for its founder
till Cuvier was born--in short, in every corner of the earth where
the investigations of civilized men have penetrated, from the Arctic
to Patagonia and the Cape of Good Hope, these relics tell us of
successive populations lying far behind our own, and belonging to
distinct periods of the world’s history.
CARBONIFEROUS PERIOD
--LOUIS FIGUIER
In the history of our globe the Carboniferous period succeeds to
the Devonian. It is in the formations of this latter epoch that we
find the fossil fuel which has done so much to enrich and civilize
the world in our own age. This period divides itself into two great
sub-periods: 1. The _Coal-measures_; and 2. The _Carboniferous
Limestone_. The first, a period which gave rise to the great deposits
of coal; the second, to most important marine deposits, most
frequently underlying the coal-fields in England, Belgium, France,
and America.
The limestone mountains, which form the base of the whole system,
attain in places, according to Professor Phillips, a thickness
of 2,500 feet. They are of marine origin, as is apparent by the
multitude of fossils they contain of Zoophytes, Radiata, Cephalopoda,
and Fishes. But the chief characteristic of this epoch is its
strictly terrestrial flora--remains of plants now become as common
as they were rare in all previous formations, announcing a great
increase of dry land.
The monuments of this era of profuse vegetation reveal themselves in
the precious Coal-measures of England and Scotland. These give us
some idea of the rich verdure which covered the surface of the earth,
newly risen from the bosom of its parent waves. It was the paradise
of terrestrial vegetation. The grand _Sigillaria_, the _Stigmaria_,
and other fern-like plants, were especially typical of this age,
and formed the woods, which were left to grow undisturbed; for as
yet no living Mammals seem to have appeared; everything indicates
a uniformly warm, humid temperature, the only climate in which
the gigantic ferns of the Coal-measures could have attained their
magnitude. Conifers have been found of this period with concentric
rings, but these rings are more slightly marked than in existing
trees of the same family, from which it is reasonable to assume that
the seasonal changes were less marked than they are with us.
Everything announces that the time occupied in the deposition of the
Carboniferous Limestone was one of vast duration. Professor Phillips
calculates that, at the ordinary rate of progress, it would require
122,400 years to produce only sixty feet of coal. Geologists believe,
moreover, that the upper Coal-measures, where bed has been deposited
upon bed for ages upon ages, were accumulated under conditions of
comparative tranquillity, but that the end of this period was marked
by violent convulsions--by ruptures of the terrestrial crust, when
the carboniferous rocks were upturned, contorted, dislocated by
faults, and subsequently partially denuded, and thus appear now in
depressions or basin-shaped concavities; and that upon this deranged
and disturbed foundation a fourth geological system, called Permian,
was constructed.
Coal, as we shall find, is composed of the mineralized remains of
the vegetation which flourished in remote ages of the world. Buried
under an enormous thickness of rocks, it has been preserved to
our days, after being modified in its inward nature and external
aspect. Having lost a portion of its elementary constituents, it has
become transformed into a species of carbon, impregnated with those
bituminous substances which are the ordinary products of the slow
decomposition of vegetable matter.
Thus, coal is the substance of the plants which formed the forests,
the vegetation, and the marshes of the ancient world, at a period
too distant for human chronology to calculate with anything like
precision.
It is a remarkable circumstance that conditions of equable and warm
climate, combined with humidity, do not seem to have been limited to
any one part of the globe, but the temperature of the whole globe
seems to have been nearly the same in very different latitudes. From
the equatorial regions up to Melville Island, in the Arctic Ocean,
where in our days eternal frost prevails--from Spitzbergen to the
centre of Africa, the carboniferous flora is identically the same.
When nearly the same plants are found in Greenland and Guinea; when
the same species, now extinct, are met with of equal development at
the equator as at the pole, we can not but admit that at this epoch
the temperature of the globe was nearly alike everywhere. What we now
call _climate_ was unknown in these geological times. There seems to
have been then only one climate over the whole globe. It was at a
subsequent period, that is, in later Tertiary times, that the cold
began to make itself felt at the terrestrial poles. Whence, then,
proceeded this general superficial warmth, which we now regard with
so much surprise? It was a consequence of the greater or nearer
influence of the interior heat of the globe. The earth was still so
hot in itself that the heat which reached it from the sun may have
been inappreciable.
Another hypothesis, which has been advanced with much less certainty
than the preceding, relates to the chemical composition of the
air during the Carboniferous period. Seeing the enormous mass of
vegetation which then covered the globe, and extended from one pole
to the other; considering, also, the great proportion of carbon and
hydrogen which exists in the bituminous matter of coal, it has been
thought, and not without reason, that the atmosphere of the period
might be richer in carbonic acid than the atmosphere of the present
day. It has even been thought that the small number of (especially
air-breathing) animals, which then lived, might be accounted for by
the presence of a greater proportion of carbonic acid gas in the
atmosphere than is the case in our own times. This, however, is
pure assumption, totally deficient in proof. What we can remark,
with certainty, as a striking characteristic of the vegetation of
the globe during this phase of its history, was the prodigious
development which it assumed. The Ferns, which in our days and in
our climate are most commonly only small perennial plants, in the
Carboniferous age sometimes presented themselves under lofty and even
magnificent forms.
Every one knows those marsh-plants with hollow, channeled, and
articulated cylindrical stems; whose joints are furnished with a
membranous, denticulated sheath, and which bear the vulgar name of
“mare’s-tail”; their fructification forming a sort of catkin composed
of many rings of scales, carrying on their lower surface sacs full of
_spores_ or seeds. These humble _Equiseta_ were represented during
the coal-period by herbaceous trees from twenty to thirty feet
high and four to six inches in diameter. Their trunks, channeled
longitudinally, and divided transversely by lines of articulation,
have been preserved to us: they bear the name of _Calamites_.
The _Lycopods_ of our age are humble plants, scarcely a yard in
height, and most commonly creepers; but the Lycopodiaceæ of the
ancient world were trees of eighty or ninety feet in height. It
was the _Lepidodendrons_ which filled the forests. Their leaves
were sometimes twenty inches long, and their trunks a yard in
diameter. Such are the dimensions of some specimens of _Lepidodendron
carinatum_ which have been found. Another Lycopod of this period, the
_Lomatophloyos crassicaule_, attained dimensions still more colossal.
The _Sigillarias_ sometimes exceeded 100 feet in height. Herbaceous
Ferns were also exceedingly abundant, and grew beneath the shade of
these gigantic trees. It was the combination of these lofty trees
with such shrubs (if we may so call them) which formed the forests of
the Carboniferous period.
How this vegetation, so imposing, both on account of the dimensions
of the individual trees and the immense space which they occupied, so
splendid in its aspect, and yet so simple in its organization, must
have differed from that which now embellishes the earth and charms
our eyes! It certainly possessed the advantage of size and rapid
growth; but how poor it was in species--how uniform in appearance! No
flowers yet adorned the foliage or varied the tints of the forests.
Eternal verdure clothed the branches of the Ferns, the Lycopods, and
Equiseta, which composed to a great extent the vegetation of the age.
The forests presented an innumerable collection of individuals, but
very few species, and all belonging to the lower types of vegetation.
No fruit appeared fit for nourishment; none would seem to have been
on the branches. Suffice it to say that few terrestrial animals
seem to have existed yet; animal life was apparently almost wholly
confined to the sea, while the vegetable kingdom occupied the land,
which at a later period was more thickly inhabited by air-breathing
animals. Probably a few winged insects (some coleoptera, orthoptera,
and neuroptera) gave animation to the air while exhibiting their
variegated colors; and it was not impossible but that many
pulmoniferous mollusca (such as land-snails) lived at the same time.
The vegetation which covered the numerous islands of the
Carboniferous sea consisted, then, of Ferns, of Equisetaceæ, of
Lycopodiaceæ, and dicotyledonous Gymnosperms. The Annularia and
Sigillariæ belong to families of the last-named class, which are now
completely extinct.
The _Annulariæ_ were small plants which floated on the surface of
fresh-water lakes and ponds; their leaves were verticillate, that
is, arranged in a great number of whorls, at each articulation of
the stem with the branches. The _Sigillariæ_ were, on the contrary,
great trees, consisting of a simple trunk, surmounted with a bunch or
panicle of slender drooping leaves, with the bark often channeled,
and displaying impressions or scars of the old leaves, which, from
their resemblance to a seal, _sigillum_, gave origin to their name.
The _Stigmariæ_, according to palæontologists, were roots of
Sigillariæ, with a subterranean fructification; all that is known of
them is the long roots which carry the reproductive organs, and in
some cases are as much as sixteen feet long.
Two other gigantic trees grew in the forests of this period: these
were _Lepidodendron carinatum_ and _Lomatophloyos crassicaule_, both
belonging to the family of Lycopodiaceæ, which now includes only very
small species. The trunk of the Lomatophloyos threw out numerous
branches, which terminated in thick tufts of linear and fleshy
leaves. The Ferns composed a great part of the vegetation of the
Coal-measure period.
The seas of this epoch included an immense number of Zoophytes,
nearly 400 species of Mollusca, and a few Crustaceans and Fishes.
Among the Fishes, _Psammodus_ and _Coccosteus_, whose massive
teeth inserted in the palate were suitable for grinding; and the
_Holoptychius_ and _Megalichthys_, are the most important. The
Mollusca are chiefly Brachiopods of great size. The _Bellerophon_,
whose convoluted shell in some respects resembles the Nautilus of our
present seas, but without its chambered shell, were then represented
by many species.
Crustaceans are rare in the Carboniferous Limestone strata; the genus
Phillipsia is the last of the Trilobites, all of which became extinct
at the close of this period. As to the Zoophytes, they consist
chiefly of Crinoids and Corals. We also have in these rocks many
Polyzoa.
Among the corals of the period we may include the genera
_Lithostrotion_ and _Lonsdalea_. Among the Polyzoa are the genera
_Fenestrella_ and _Polypora_. Lastly, to these we may add a group
of animals which will play a very important part and become
abundantly represented in the beds of later geological periods, but
which already abounded in the seas of the Carboniferous period. We
speak of the _Foraminifera_, microscopic animals, which clustered
either in one body or divided into segments, and covered with a
calcareous, many-chambered shell, as _Fusulina cylindrica_. These
little creatures, which, during the Jurassic and Cretaceous periods,
formed enormous banks and entire masses of rock, began to make their
appearance in the period which now engages our attention.
This terrestrial period is characterized, in a remarkable manner, by
the abundance and strangeness of the vegetation which then covered
the islands and continents of the whole globe. Upon all points of the
earth, as we have said, this flora presented a striking uniformity.
In comparing it with the vegetation of the present day, the learned
French botanist, M. Brongniart, who has given particular attention
to the flora of the Coal-measures, has arrived at the conclusion
that it presented considerable analogy with that of the islands
of the equatorial and torrid zone, in which a maritime climate and
elevated temperature exist in the highest degree. It is believed that
islands were very numerous at this period; that, in short, the dry
land formed a sort of vast archipelago upon the general ocean, of no
great depth, the islands being connected together and formed into
continents as they gradually emerged from the ocean.
This flora, then, consists of great trees, and also of many
smaller plants, which would form a close, thick turf, or sod,
when partially buried in marshes of almost unlimited extent. M.
Brongniart indicates, as characterizing the period, 500 species
of plants which now attain a prodigious development. The ordinary
dicotyledons and monocotyledons--that is, plants having seeds with
two lobes in germinating and plants having one seed-lobe--are
almost entirely absent; the cryptogamic, or flowerless plants,
predominate; especially Ferns, Lycopodiaceæ, and Equisetaceæ--but
of forms insulated and actually extinct in these same families. A
few dicotyledonous gymnosperms, or naked-seed plants forming genera
of Conifers, have completely disappeared, not only from the present
flora, but since the close of the period under consideration, there
being no trace of them in the succeeding Permian flora. Such is a
general view of the features most characteristic of the coal-period,
and of the Primary epoch in general. It differs, altogether and
absolutely, from that of the present day; the climatic condition of
these remote ages of the globe, however, enables us to comprehend the
characteristics which distinguish its vegetation. A damp atmosphere,
of an equable rather than an intense heat like that of the tropics,
a soft light veiled by permanent fogs, were favorable to the growth
of this peculiar vegetation, of which we search in vain for anything
strictly analogous in our own days. The nearest approach to the
climate and vegetation proper to the geological period which now
occupies our attention would probably be found in certain islands,
or on the littoral of the Pacific Ocean--the island of Chloë, for
example, where it rains during 300 days in the year, and where the
light of the sun is shut out by perpetual fogs; where arborescent
Ferns form forests, beneath whose shade grow herbaceous Ferns, which
rise three feet and upward above a marshy soil; which gives shelter
also to a mass of cryptogamic plants, greatly resembling, in its
main features, the flora of the Coal-measures. This flora was, as
we have said, uniform and poor in its botanic genera, compared to
the abundance and variety of the flora of the present time; but the
few families of plants which existed then included many more species
than are now produced in the same countries. The fossil Ferns of the
coal-series in Europe, for instance, comprehend about 300 species,
while all Europe now only produces fifty. The gymnosperms, which now
muster only twenty-five species in Europe, then numbered more than
120.
Calamites are among the most abundant fossil plants of the
Carboniferous period, and occur also in the Devonian. They are
preserved as striated, jointed, cylindrical, or compressed stems,
with fluted channels or furrows at their sides, and sometimes
surrounded by a bituminous coating, the remains of a cortical
integument. They were originally hollow, but the cavity is usually
filled up with a substance into which they themselves have been
converted.
If, during the coal-period, the vegetable kingdom had reached its
maximum, the animal kingdom, on the contrary, was poorly represented.
Some remains have been found, both in America and Germany, consisting
of portions of the skeleton and the impressions of the footsteps
of a Reptile, which has received the name of Archegosaurus. Among
the animals of this period we find a few Fishes, analogous to
those of the Devonian formation. These are the _Holoptychius_ and
_Megalichthys_, having jawbones armed with enormous teeth. Scales
of _Pygopterus_ have been found in the Northumberland Coal-shale at
Newsham Colliery, and also in the Staffordshire Coal-shale. Some
winged insects would probably join this slender group of living
beings. It may then be said with truth that the immense forests and
marshy plains, crowded with trees, shrubs, and herbaceous plants,
which formed on the innumerable isles of the period a thick and
tufted sward, were almost destitute of animals.
Coal, as we have said, is only the result of a partial decomposition
of the plants which covered the earth during a geological period
of immense duration. No one, now, has any doubt that this is its
origin. In coal-mines it is not unusual to find fragments of the very
plants whose trunks and leaves characterize the Coal-measures, or
Carboniferous era. Immense trunks of trees have also been met with
in the middle of a seam of coal. In order to explain the presence
of coal in the depths of the earth, there are only two possible
hypotheses. This vegetable débris may either result from the burying
of plants brought from afar and transported by river or maritime
currents, forming immense rafts, which may have grounded in different
places and been covered subsequently by sedimentary deposits; or the
trees may have grown on the spot where they perished, and where they
are now found.
Can the coal-beds result from the transport by water, and burial
under ground, of immense rafts formed of the trunks of trees? The
hypothesis has against it the enormous height which must be conceded
to the raft, in order to form coal-seams as thick as some of those
which are worked in our collieries. If we take into consideration the
specific gravity of wood, and the amount of carbon it contains, we
find that the coal-deposits can only be about seven-hundredths of the
volume of the original wood and other vegetable materials from which
they are formed. If we take into account, besides, the numerous voids
necessarily arising from the loose packing of the materials forming
the supposed raft, as compared with the compactness of coal, this may
fairly be reduced to five-hundredths. A bed of coal, for instance,
sixteen feet thick, would have required a raft 310 feet high for its
formation. These accumulations of wood could never have arranged
themselves with sufficient regularity to form those well-stratified
coal-beds, maintaining a uniform thickness over many miles, and that
are seen in most coal-fields to lie one above another in succession,
separated by beds of sandstone or shale. And even admitting the
possibility of a slow and gradual accumulation of vegetable débris,
like that which reaches the mouth of a river, would not the plants
in that case be buried in great quantities of mud and earth? Now,
in most of our coal-beds the proportion of earthy matter does not
exceed fifteen per cent of the entire mass. If we bear in mind,
finally, the remarkable parallelism existing in the stratification
of the coal-formation, and the state of preservation in which the
impressions of the most delicate vegetable forms are discovered, it
will, we think, be proved to demonstration that those coal-seams have
been formed in perfect tranquillity. We are, then, forced to the
conclusion that coal results from the mineralization of plants which
has taken place on the spot; that is to say, in the very place where
the plants lived and died.
It was suggested long ago by Bakewell, from the occurrence of the
same peculiar kind of fireclay under each bed of coal, that it was
the soil proper for the production of those plants from which coal
has been formed.