Draw two lines on your map, the upper one running from the mouth of the
St. Lawrence westward nearly to St. Paul on the Mississippi, and the
lower one from the neighborhood of St. John's in Newfoundland running
southwesterly about to the point where the Wisconsin joins the
Mississippi, but jutting down to form an extensive peninsula comprising
part of the States of Indiana and Illinois, and you include between them
all of the United States which existed at the close of the Devonian
period. The upper line rests against the granite hills dividing the
Silurian and Devonian deposits of the British Possessions to the north
from those of the United States to the south, Canada itself consisting,
in great part, of the granite ridge.
How far the early deposits extended to the north of the Laurentian
Hills, as well as the outline of that portion of the continent in those
times, remains still very problematical; but the investigations thus far
undertaken in those regions would lead to the supposition that the same
granite upheaval which raised Canada stretched northward in a broad,
low ridge of land, widening in its upper part and extending to the
neighborhood of Bathurst Inlet and King William's Island, while on
either side of it to the east and west the Silurian and Devonian
deposits extended far toward the present outlines of the continent.
Indeed, our geological surveys, as well as the information otherwise
obtained concerning the primitive condition of North America and the
gradual accessions it has received in more recent periods, point to a
very early circumscription of the area which, in the course of time, was
to become the continent we now inhabit, with its modern features.[A]
[Footnote A: It would be impossible to encumber the pages of the
_Atlantic Monthly_ with references to all the authorities on which such
geological results rest. They are drawn from the various State Surveys,
including that of the mineral lands of Lake Superior, and other more
general works on American geology.]
Not only from the geology of America, but from that of Europe also, it
would seem that the position of the continents was sketched out very
early in the progressive development of the physical constitution of our
earth. It is true that in the present state of our knowledge such wide
generalizations must be taken with caution, and held in abeyance to the
additional facts which future investigations may develop. But thus far
the results certainly do not sustain the theories which have lately
found favor among geologists, of entire changes in the relative
distribution of land and sea and in the connection of continents with
one another; on the contrary, it would appear, that, in accordance with
the laws of all organic progress, arising from a fixed starting-point
and proceeding through regular changes toward a well-defined end, the
continents have grown steadily and consistently from the beginning,
through successive accessions in a definite direction, to their present
form and Organic correlations. If, indeed, there is any meaning in the
remarkably symmetrical combinations of the double twin continents in
the Eastern Hemisphere, so closely soldered in their northern half, as
contrasted with the single pair in the Western Hemisphere, isolated in
their position, but so strikingly similar in their Outlines, they must
be the result of a progressive and predetermined growth already hinted
at in the relative position and gradual increase of the first lands
raised above the level of the ocean.
However this may be, there can be no doubt that we now know with
tolerable accuracy the limits of the land raised above the water at that
period in the present United States. Let us see, then, what we inclose
between oar two lines. We have Newfoundland and Nova Scotia, the greater
part of New England, the whole of New York, a narrow strip along the
north of Ohio, a great part of Indiana and Illinois, and nearly the
whole of Michigan and Wisconsin.
Within this region lie all the Great Lakes. The origin of these large
troughs, holding such immense sheets of fresh water, remains still the
subject of discussion and investigation among geologists. It has been
supposed that in the primitive configuration of the globe, when the
formation of those depressions at the poles in which the Arctic seas are
accumulated gave rise to a corresponding protrusion at the equator, the
curve thus produced throughout the North Temperate Zone may have forced
up the Canada granite, and have caused, at the same time, those rents
in the earth's surface now filled by the Canada lakes; and this view
is sustained by the fact that there is a belt of lakes, among which,
however, the Canada lakes are far the largest, all around the world in
that latitude. The geological phenomena connected with all these lakes
have not, however, been investigated with sufficient accuracy and
detail, nor has there been any comparison of them extensive and
comprehensive enough to justify the adoption of any theory respecting
their origin. In an excursion to Lake Superior, some years since, I
satisfied myself that the position and outline of that particular lake
had their immediate cause in several distinct systems of dikes which
intersect its northern shore, and have probably cut up the whole tract
of rock over the space now filled by that wonderful sheet of fresh water
in such a way as to destroy its continuity, to produce depressions, and
gradually create the excavation which now forms the basin of the lake.
How far the same causes have been effectual in producing the other large
lakes I am unable to say, never having had the opportunity of studying
their formation with the same care.
The existence of the numerous smaller lakes running north and south in
the State of New York, as the Canandaigua, Seneca, Cayuga, etc., is more
easily accounted for. Slow and gradual as was the process by which
all that region was lifted above the ocean, it was, nevertheless,
accompanied by powerful dislocations of the stratified deposits, as we
shall see when we examine them with reference to the local phenomena
connected with them. To these dislocations of the strata we owe the
transverse cracks across the central part of New York, which needed
only the addition of the fresh water poured into them by the rains to
transform them into lakes.
I shall not attempt any account of the differences between the animals
of the Devonian period and those of the Silurian period, because they
consist of structural details difficult to present in a popular form and
uninteresting to all but the professional naturalist. Suffice it to say,
that, though the organic world had the same general character in these
two closely allied periods, yet its representatives in each were
specifically distinct, and their differences, however slight, are as
constant and as definitely marked as those between more widely separated
creations.
At the close of the Devonian period, several upheavals occurred of great
significance for the future history of America. One in Ohio raised the
elevated ground on which Cincinnati now stands; another hill lifted
its granite crest in Missouri, raising with it an extensive tract of
Silurian and Devonian deposits; while a smaller one, which does not
seem, however, to have disturbed the beds about it so powerfully, broke
through in Arkansas. At the same time, elevations took place toward the
East,--the first links, few and detached, in the great Alleghany chain
which now raises its rocky wall from New England to Alabama.
In the Ohio hill, the granite did not break through, though the force of
the upheaval was such as to rend asunder the Devonian deposits, for we
find them lying torn and broken about the base of the hill; while the
Silurian beds, which should underlie them in their natural position,
form its centre and summit. This accounts for the great profusion of
Silurian organic remains in that neighborhood. Indeed, there is no
locality which forces upon the observer more strongly the conviction of
the profusion and richness of the early creation; for one may actually
collect the remains of Silurian Shells and Crustacea by cart-loads
around the city of Cincinnati. A naturalist would find it difficult to
gather along any modern sea-shore, even on tropical coasts, where marine
life is more abundant than elsewhere, so rich a harvest, in the same
time, as he will bring home from an hour's ramble in the environs of
that city.
These elevations naturally gave rise to depressions between themselves
and the land on either side of them, and caused also so many
counter-slopes dipping toward the uniform southern slope already formed
at the north. Thus between the several new upheavals, as well as between
them all and the land to the north of them, wide basins or troughs were
formed, inclosed on the south, west, and east by low hills, (for these
more recent eruptions were, like all the early upheavals, insignificant
in height,) and bounded on the north by the more ancient shores of the
preceding ages.
These were the inland seas of the Carboniferous period. Here, again, we
must infer the successive stages of a history which we can read only
in its results. Shut out from the ocean, these shallow sea-basins were
gradually changed by the rains to fresh-water lakes; the lakes, in their
turn, underwent a transformation, becoming filled, in the course of
centuries, with the materials worn away from their shores, with the
_débris_ of the animals which lived and died in their waters, as well
as with the decaying matter from aquatic plants, till at last they were
changed to spreading marshes, and on these marshes arose the gigantic
fern-vegetation of which the first forests chiefly consisted. Such are
the separate chapters in the history of the coal-basins of Illinois,
Missouri, Pennsylvania, New England, and Nova Scotia. First inland seas,
then fresh-water lakes, then spreading marshes, then gigantic forests,
and lastly vast storehouses of coal for the human race.
Although coal-beds are by no means peculiar to the Carboniferous period,
since such deposits must be formed wherever the decay of vegetation is
going on extensively, yet it would seem that coal-making was the great
work in that age of the world's physical history. The atmospheric
conditions, so far as we can understand them, were then especially
favorable to this result. Though the existence of such an extensive
terrestrial vegetation shows conclusively that an atmosphere must have
been already established, with all the attendant phenomena of light,
heat, air, moisture, etc., yet it is probable that this atmosphere
differed from ours in being very largely charged with carbonic acid.
We should infer this from the nature of the animals characteristic of
the period; for, though land-animals were introduced, and the organic
world was no longer exclusively marine, there were as yet none of
the higher beings in whom respiration is an active process. In all
warm-blooded animals the breathing is quick, requiring a large
proportion of oxygen in the surrounding air, and indicating by its
rapidity the animation of the whole system; while the slow-breathing,
cold-blooded animals can live in an air that is heavily loaded with
carbon. It is well known, however, that, though carbon is so deadly to
higher animal life, plants require it in great quantities; and it would
seem that one of the chief offices of the early forests was to purify
the atmosphere of its undue proportion of carbonic acid, by absorbing
the carbon into their own substance, and eventually depositing it as
coal in the soil.
Another very important agent in the process of purifying the atmosphere,
and adapting it to the maintenance of a higher organic life, is found in
the deposits of lime. My readers will excuse me, if I introduce here a
very elementary chemical fact to explain this statement. Limestone is
carbonate of calcium. Calcium is a metal, fusible as such, and, forming
a part of the melted masses within the earth, it was thrown out with the
eruptions of Plutonic rocks. Brought to the air, it would appropriate
a certain amount of oxygen, and by that process would become oxide of
calcium, in which condition it combines very readily with carbonic acid.
Thus it becomes carbonate of lime; and all lime deposits played an
important part in establishing the atmospheric proportions essential to
the existence of the warm-blooded animals.
Such facts remind us how far more comprehensive the results of science
will become when the different branches of scientific investigation are
pursued in connection with each other. When chemists have brought their
knowledge out of their special laboratories into the laboratory of the
world, where chemical combinations are and have been through all time
going on in such vast proportions,--when physicists study the laws
of moisture, of clouds and storms, in past periods as well as in the
present,--when, in short, geologists and zoologists are chemists and
physicists, and _vice versa_,--then we shall learn more of the changes
the world has undergone than is possible now that they are separately
studied.
It may be asked, how any clue can be found to phenomena so evanescent as
those of clouds and moisture. But do we not trace in the old deposits
the rainstorms of past times? The heavy drops of a passing shower, the
thick, crowded tread of a splashing rain, or the small pinpricks of a
close and fine one,--all the story, in short, of the rising vapors,
the gathering clouds, the storms and showers of ancient days, we find
recorded for us in the fossil rain-drops; and when we add to this the
possibility of analyzing the chemical elements which have been absorbed
into the soil, but which once made part of the atmosphere, it is not too
much to hope that we shall learn something hereafter of the meteorology
even of the earliest geological ages.
The peculiar character of the vegetable tissue in the trees of the
Carboniferous period, containing, as it did, a large supply of
resin drawn from the surrounding elements, confirms the view of the
atmospheric conditions above stated; and this fact, as well as the damp,
soggy soil in which the first forests must have grown, accounts for the
formation of coal in greater quantity and more combustible in quality
than is found in the more recent deposits. But stately as were those
fern forests, where plants which creep low at our feet to-day, or are
known to us chiefly as underbrush, or as rushes and grasses in swampy
grounds, grew to the height of lofty trees, yet the vegetation was of an
inferior kind.
There has been a gradation in time for the vegetable as well as the
animal world. With the marine population of the more ancient geological
ages we find nothing but sea-weeds,--of great variety, it is true, and,
as it would seem, from some remains of the marine Cryptogams in early
times, of immense size, as compared with modern sea-weeds. But in the
Carboniferous period, the plants, though still requiring a soaked and
marshy soil, were aërial or atmospheric plants: they were covered with
leaves; they breathed; their fructification was like that which now
characterizes the ferns, the club-mosses, and the so-called "horse-tail
plants," (_Equisetaceae,_) those grasses of low, damp grounds remarkable
for the strongly marked articulations of the stem.
These were the lords of the forests all over the world in the
Carboniferous period. Wherever the Carboniferous deposits have been
traced, in the United States, in Canada, in England, France, Belgium,
Germany, in New Holland, at the Cape of Good Hope, and in South America,
the general aspect of the vegetation has been found to be the same,
though characterized in the different localities by specific
differences of the same nature as those by which the various floras are
distinguished now in different parts of the same zone. For instance, the
Temperate Zone throughout the world is characterized by certain families
of trees: by Oaks, Maples, Beeches, Birches, Pines, etc.; but the Oaks,
Maples, Beeches, Birches, and the like, of the American flora in that
latitude differ in species from the corresponding European flora. So
in the Carboniferous period, when more uniform climatic conditions
prevailed throughout the world, the character of the vegetation showed a
general unity of structure everywhere; but it was nevertheless broken up
into distinct botanical provinces by specific differences of the same
kind as those which now give such diversity of appearance to the
vegetation of the Temperate Zone in Europe as compared with that of
America, or to the forests of South America as compared with those of
Africa.
There can be no doubt as to the true nature of the Carboniferous
forests; for the structural character of the trees is as strongly marked
in their fossil remains as in any living plants of the same character.
We distinguish the Ferns not only by the peculiar form of their leaves,
often perfectly preserved, but also by the fructification on the lower
surface of the leaves, and by the distinct marks made on the stem at
their point of juncture with it. The leaf of the Fern, when falling,
leaves a scar on the stem varying in shape and size according to the
kind of Fern, so that the botanist readily distinguishes any particular
species of Fern by this means,--a birth-mark, as it were, by which he
detects the parentage of the individual. Another indication, equally
significant, is found in the tubular structure of the wood in Ferns. On
a vertical section of any well-preserved Fern-trunk from the old forests
the little tubes may be seen very distinctly running up its length; or,
if it be cut through transversely, they may be traced by the little
pores like dots on the surface. Trees of this description are found in
the Carboniferous marshes, standing erect and perfectly preserved, with
trunks a foot and a half in diameter, rising to a height of many feet.
Plants so strongly bituminous as the Ferns, when they equalled in size
many of our present forest-trees, naturally made coal deposits of the
most combustible quality. It is true that we find the anthracite coal of
the same period with comparatively little bituminous matter; but this is
where the bitumen has been destroyed by the action of the internal heat
of the earth.
Next to the Ferns, the Club-Mosses (_Lycopodiacae_) seem to have
contributed most largely to the marsh-forests. They were characterized,
then, as now, by the small size of the leaves growing close against the
stem, so that the stem itself, though covered with leaves, looks
almost naked, like the stem of the Cactus. Beside these, there are the
tree-like Equiseta, in which we find the articulations on the trunk
corresponding exactly to those now so characteristic of those
marsh-grasses which are the modern representatives of this family of
plants, with cone-like fructifications on the summit of the stem.
I would merely touch here upon a subject which does not belong to my own
branch of Natural History, but is of the greatest interest in botanical
research, namely, the gradation of plants in the geological ages, and
the combination of characters in some of the earlier vegetable forms,
corresponding to that already noticed in the ancient animal types. For
instance, in the Carboniferous period we have only Cryptogams, Ferns,
Lycopodiacae, and Equisetaceae. In the middle geological ages, Conifers
are introduced, the first flowering plant known on earth, but in which
the flower is very imperfect as compared with those of the higher
groups. The Coniferae were chiefly represented in the middle periods by
the Cycadae, that peculiar group of Coniferae, resembling Pines in their
structure, but recalling the Ferns by their external appearance. The
stem is round and short, its surface being covered with scars similar to
those of the Ferns; while on the summit are ten or more leaves, fan-like
and spreading when their growth is complete, but rolled up at first,
like Fern-leaves before they expand. Their fruit resembles somewhat the
Pine-Apple.
The mode of growth of the Coniferae recalls a feature of the
Equisetaceae also, in the tufts of little leaves which appear in whorls
at regular intervals along the length of the stem in proportion as
it elongates, reminding one of the articulations on the stem of the
Equisetaceae. The first cone also appears on the summit of the stem,
like the terminal cone in the Equisetaceae and the Club-Mosses. Thus
in certain types of the vegetable, as well as the animal creation of
earlier times, there was a continuation of features, afterwards divided
and presented in separate groups. In the present times, no one of
these families of plants overlaps the others, but each has a distinct
individual character of its own.
At the close of the middle geological ages and the opening of the
Tertiary periods, the Monocotyledons become abundant, the first plants
with flower and inclosed seed, though with no true floral envelope: but
not until the two last epochs of the Tertiary age do we find in any
number the Dicotyledonous plants, in which flower and fruit rise to
their highest perfection. Thus there has been a procession of plants
from their earliest introduction to the present day, corresponding to
their botanical rank as they now exist, so that the series of gradation
in the Vegetable Kingdom, as well as the Animal Kingdom, is the same,
whether founded upon succession in time or upon comparative structural
rank.
Some attempt has been made to reproduce under an artistic form the
aspect of the world in the different geological ages, and to present in
single connected pictures the animal and vegetable world of each period.
Professor F. Unger, of Vienna, has prepared a collection of fourteen
such sketches, entitled, "Tableaux Physionomiques de la Végétation des
Diverses Périodes du Monde Primitif."
First, we have the Devonian shores, with spreading fields of sea-weed
and numbers of the club-shaped Algae of gigantic size. He has ventured,
also, to represent a few trees, with scanty foliage; but I believe their
existence at so early a period to be very problematical.
Next comes the Carboniferous forest, with still pools of water lying
between the Fern-trees, which, much as they affect damp, swampy grounds,
seem scarcely able to find foothold on the dripping earth. Their trunks,
as well as those of the Club-Moss trees which make the foreground of the
picture, stand up free from any branches for many feet above the ground,
giving one a glimpse between them into the dim recesses of this quiet,
watery wood, where the silence was unbroken by the song of birds or the
hum of insects. We shall find, it is true, when we give a glance at the
animals of this time, that certain insects made their appearance with
the first terrestrial vegetation; but they were few in number and of a
peculiar kind, such as thrive now in low, wet lands.
Upon this follow a number of sketches introducing us to the middle
periods, where the land is higher and more extensive, covered chiefly
with Pine forests, beneath which grows a thick carpet of underbrush,
consisting mostly of Grasses, Rushes, and Ferns. Here and there one of
the gigantic reptiles of the time may be seen sunning himself on
the shore. One of these sketches shows us such a creature hungrily
inspecting a pool where Crinoids, with their long stems, large,
closely-coiled Chambered Shells, and Brachiopods, the Oysters and
Clams of those days, offer him a tempting repast. Here and there a
Pterodactyl, the curious winged reptile of the later middle periods,
stretches its long neck from the water, and birds also begin to make
their appearance.
After these come the Tertiary periods: the Eocene first, where the
landscape is already broken up by hills and mountains, clothed with
a varied vegetation of comparatively modern character. Lily-pads are
floating on the stream which makes the central part of the picture;
large herds of the Palaeotherium, the ancient Pachyderm, reconstructed
with such accuracy by Cuvier, are feeding along its banks; and a tall
bird of the Heron or Pelican kind stands watching by the water's edge.
In the Miocene the vegetation looks still more familiar, though the
Elephants roaming about in regions of the Temperate Zone, and the huge
Salamanders crawling out of the water, remind us that we are still far
removed from present times. Lastly, we have the ice period, with the
glaciers coming down to the borders of a river where large troops of
Buffalo are drinking, while on the shore some Bears are feasting on the
remains of a huge carcass.
It is, however, with the Carboniferous age that we have to do at
present, and I will not anticipate the coming chapters of my story by
dwelling now on the aspect of the later periods. To return, then, to the
period of the coal, it would seem that extensive freshets frequently
overflowed the marshes, and that even after many successive forests
had sprung up and decayed upon their soil, they were still subject to
submergence by heavy floods. These freshets, at certain intervals,
are not difficult to understand, when we remember, that, beside the
occasional influx of violent rains, the earth was constantly undergoing
changes of level, and that a subsidence or upheaval in the neighborhood
would disturb the equilibrium of the waters, causing them to overflow
and pour over the surface of the country, thus inundating the marshes
anew.
That such was the case we can hardly doubt, after the facts revealed
by recent investigations of the Carboniferous deposits. In some of the
deeper coal-beds there is a regular alternation between layers of coal
and layers of sand or clay; in certain localities, as many as ten,
twelve, and even fifteen coal-beds have been found alternating with as
many deposits of clay or mud or sand; and in some instances, where the
trunks of the trees are hollow and have been left standing erect, they
are filled to the brim, or to the height of the next layer of deposits,
with the materials that have been swept over them. Upon this set of
deposits comes a new bed of coal with the remains of a new forest, and.
above this again a layer of materials left by a second freshet, and so
on through a number of alternate strata. It is evident from these facts
that there have been a succession of forests, one above another, but
that in the intervals of their growth great floods have poured over the
marshes, bringing with them all kinds of loose materials, such as sand,
pebbles, clay, mud, lime, etc., which, as the freshets subsided, settled
down over the coal, filling not only the spaces between such trees as
remained standing, but even the hollow trunks of the trees themselves.
Let us give a glance now at the animals which inhabited the waters of
this period. In the Radiates we shall not find great changes; the three
classes are continued, though with new representatives, and the Polyp
Corals are increasing, while the Acalephian Corals, the Kugosa and
Tabulata, are diminishing. The Crinoids were still the most prominent
representatives of the class of Echinoderms, though some resembling the
Ophiurans and Echinoids (Sea-Urchins) began to make their appearance.
The adjoining wood-cut represents a characteristic Crinoid of the
Carboniferous age.
[Illustration]
Among the Mollusks, Brachiopods are still prominent, one new genus among
them, the Productus, being very remarkable on account of the manner in
which one valve rises above the other. The wood-cut below represents such
a shell, looked at from the side of the flat valve, showing the straight
cut of the line of juncture between the valves and the rising curve of
the opposite one, which looks like a hooked beak when seen in profile.
[Illustration]
Other species of Bivalves were also introduced, approaching more
nearly our Clams and Oysters, or, as they are called in scientific
nomenclature, the Lamellibranchiates. They differ from the Brachiopods
chiefly in the higher character of their breathing-apparatus; for they
have free gills, instead of the net-work of vessels on the lining skin
which serves as the organ of respiration in the Brachiopods. We shall
always find, that, in proportion as the functions are distinct, and, as
it were, individualized by having special organs appropriated to them,
animals rise in the scale of structure. The next class of Mollusks, the
Gasteropods, or Univalves, with spiral shells, were numerous, but,
from their brittle character, are seldom found in a good state of
preservation.
The Chambered Shells, or the Cephalopods, represented chiefly in the
earlier periods by the straight Orthoceratites described in a previous
article, are now curled in a close coil, and the internal structure
of their chambers has become more complicated. The subjoined wood-cut
represents a characteristic Chambered Shell of the Carboniferous age.
Goniatites is the scientific name of these later forms. If we had looked
for them in the Devonian period, we should have found many with looser
coils than these, and some only slightly curved in the shape of a horn.
These, as well as the perfectly straight forms, still exist in the coal
period, but the Goniatites with close whorls are the more numerous and
more characteristic.
[Illustration]
The Articulates have gained their missing class since the close of the
Devonian period, for Insects have come in, and that division of the
Animal Kingdom is therefore complete, and represented by three classes,
as it is at present. Of the Worms little can be said; their traces are
found as before, but they are very imperfectly preserved. There are
still Trilobites, but they are very few in number, and other groups of
Crustacea have been added.
One of the most prominent of these new types bears a striking
resemblance to the Horse-Shoe Crab of present times.
[Illustration]
[Illustration]
I here present one of our common Horse-Shoe Crabs above one of these
old-world Crustaceans, and it will be seen, that, while the latter
preserves some of the Trilobitic characters, such as the marked
articulations on the posterior part of the body and their division into
three lobes, yet in the prominence of its anterior shield, its more
elongated form, and tapering extremity, it resembles its modern
representative. In some of them, however, there is no such sharp point
as is here figured, and the body terminates bluntly. There were a large
number of these Entomostraca in the Carboniferous period, a group which
is chiefly represented among living Crustacea by an exceedingly minute
kind of Shrimp; but in those days they were of the size of our Crabs and
Lobsters, or even larger, and the Horse-Shoe Crab still maintains their
claim to a place among the larger and more conspicuous members of the
class.
The Insects were few, and, as I have said above, of a kind which seeks a
moist atmosphere, or whose larvae live altogether in water. They are not
usually well preserved, as will be seen from the broken character of
the one here represented, although the wood-cut is made from a better
specimen than is often found. We have, however, remains enough
to establish unquestionably the fact of their existence in the
Carboniferous period, and to show us that the type of Articulates was
already represented by all its classes.
[Illustration]
Not so with the Vertebrates. Fishes abound, but their class still
consists, as before, of the Ganoids, those fishes of the earlier
periods built on the Gar-Pike and Sturgeon pattern, and the Selachians,
represented now by Sharks and Skates. In the Carboniferous period we
begin to find perfectly preserved specimens of the Ganoids, and the
adjoining wood-cut represents such a one. Of the old type of Selachians
we have again one lingering representative in our own times to give us
the clue to its ancestors,--as the Gar-Pike explains the old Ganoids,
and the Chambered Nautilus helps us to understand the Chambered Shells
of past times. The so-called Port-Jackson Shark has features which were
very characteristic of the Carboniferous Sharks and are lost in the
modern ones, so that it affords us a sort of link, as it were, and a
measure of comparison, between those now living and the more ancient
forms. It is an interesting fact that this only living representative of
the Carboniferous Shark should be found in New Holland, because it is
there, in that isolated continent, left apart, as it would seem, for a
special purpose, that we find reproduced for us most fully the character
of the Animal Kingdom in earlier creations.
[Illustration]
The first Mammalia in the world were pouched animals, having that
extraordinary attachment to the mother after birth which characterizes
the Kangaroo. In New Holland almost all the Mammalia are pouched, and
have also the imperfect organization of the brain, as compared with the
other Mammalia, which accompanies that peculiar structural feature; and
although the American Opossum makes an exception to the rule, it is
nevertheless true that this type of the Animal Kingdom is now confined
almost exclusively to New Holland. Whether this living picture of old
creations in modern garb was meant to be educational for man or not, it
is at least well that we should take advantage of it in learning all it
has to teach us of the relations between the organic world of past and
present times.
There were a great variety of the Selachians in the Carboniferous
period. The wood-cuts below represent a tooth and a spine from one of
the most characteristic groups, but I have not thought it worth while to
enumerate or to figure others here, for there are no perfect specimens,
and their structural differences consist chiefly in the various form and
appearance of the teeth, scales, and spines, and would be uninteresting
to most of my readers. I would refer the more scientific ones, who may
care to know something of these details, to my investigations on Fossil
Fishes, published many years since under the title of "Recherches sur
les Poissons Fossiles."
[Illustration]
[Illustration]
Although the Vertebrate division of the Animal Kingdom still waited for
its higher classes, yet it had received one important addition since
the Silurian and Devonian periods. The Carboniferous marshes were not
without their reptilian inhabitants; but they were Reptiles of the
lowest class, the so-called Amphibians, those which are hatched from the
egg in an immature condition, undergoing metamorphosis after birth. They
have no hard scales, and lay a large number of eggs. I am unable to
present any figure of one of these ancient Reptiles, as they are found
in so imperfect a state of preservation that no plates have been made
from them. I would add in connection with this subject that I believe
a large number of animals found in the Carboniferous deposits, and
referred to the class of Reptiles, to be Fishes allied to Saurians.
Before leaving the Carboniferous period, let us see what territory the
United States has conquered from the Ocean during that time. All
its central portion, from Canada to Alabama, and from Western Iowa,
Missouri, and Arkansas to Eastern Virginia, was raised above the water.
But as yet the Alleghanies and the Rocky Mountains did not exist; a
great gulf ran up to the mouth of the Ohio, for the Mississippi had not
yet accumulated the soil for the fertile valley through which it was to
take its southern course; the Coral-Builders had still their work to do
in constructing the peninsula of Florida; and, indeed, all the borders
of the continent of North America, as well as a large part of its
Western territory, were still to be added. But although its central
portion held its ground and was never submerged again, yet the continent
was slowly subsiding during the middle geological periods, so that,
instead of enlarging gradually by the increase of deposits, its limits
remained much the same.
This accounts for the very scanty traces to be found in America of
the secondary deposits; for the Permian, Triassic, and Jurassic beds,
instead of being raised to form successive shores, along which their
deposits could be accumulated in regular sequence, as had been the case
with the Azoic, Silurian, and Devonian deposits in the northern part of
the United States, were constantly sinking, so that the Triassic settled
above the Permian, the Jurassic above the Triassic, and so on, each set
of strata thus covering over and concealing the preceding one. Though we
find the stratified rocks of these periods cropping out here and there,
where some violent disturbance or the abrading action of water has
torn asunder or worn away the overlying strata, yet we never find
them consecutively over any extensive region; and it is not till the
Cretaceous and earlier Tertiary periods that we find again a regular
succession of deposits around the shores of the continent, marking its
present outlines. It is, then, in Europe, where the sequence of their
beds is most complete, that we must seek to decipher the history of the
middle geological ages; and therefore, when I meet my readers again,
it will be in the Old World of civilization, though more recent in its
physical features than the one we leave.
* * * * *