Vestiges of the Natural History of Creation
by Robert Chambers · English · Gutenberg #7116 · 498,151 chars · public domain (US)
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Title: Vestiges of the Natural History of Creation
Author: Robert Chambers
Release date: December 1, 2004 [eBook #7116]
Most recently updated: September 7, 2018
Language: English
Other information and formats: www.gutenberg.org/ebooks/7116
Credits: Transcribed from the 1844 John Churchill edition by David Price
*** START OF THE PROJECT GUTENBERG EBOOK VESTIGES OF THE NATURAL HISTORY OF CREATION ***
Transcribed from the 1844 John Churchill edition by David Price, email
ccx074@pglaf.org
VESTIGES
OF
THE NATURAL HISTORY
OF
CREATION.
* * * * *
LONDON:
JOHN CHURCHILL, PRINCES STREET, SOHO.
M DCCC XLIV.
CONTENTS.
PAGE
The Bodies of Space—Their arrangements and formation 1
Constituent materials of the Earth and of the other Bodies 27
of Space
The Earth formed—Era of the Primary Rocks 44
Commencement of Organic Life—Sea Plants, Corals, etc. 54
Era of the Old Red Sandstone—Fishes abundant. 66
Secondary Rocks. Era of the Carboniferous Formation.—Land 76
formed—Commencement of Land Plants
Era of the New Red Sandstone—Terrestrial Zoology commences 94
with Reptiles—First traces of Birds
Era of the Oolite—Commencement of Mammalia 105
Era of the Cretaceous Formation 116
Era of the Tertiary Formation—Mammalia abundant 125
Era of the Superficial Formations—Commencement of present 134
Species
General Considerations respecting the Origin of the 145
Animated Tribes
Particular Considerations respecting the Origin of the 165
Animated Tribes
Hypothesis of the Development of the Vegetable and Animal 191
Kingdoms
Macleay System of Animated Nature—This System considered in 236
connexion with the Progress of Organic Creation, and as
indicating the natural status of Man
Early History of Mankind 277
Mental Constitution of Animals 324
Purpose and General Condition of the Animated Creation 361
Note Conclusory 387
THE BODIES OF SPACE,
THEIR ARRANGEMENTS AND FORMATION.
IT is familiar knowledge that the earth which we inhabit is a globe of
somewhat less than 8000 miles in diameter, being one of a series of
eleven which revolve at different distances around the sun, and some of
which have satellites in like manner revolving around them. The sun,
planets, and satellites, with the less intelligible orbs termed comets,
are comprehensively called the solar system, and if we take as the
uttermost bounds of this system the orbit of Uranus (though the comets
actually have a wider range), we shall find that it occupies a portion of
space not less than three thousand six hundred millions of miles in
extent. The mind fails to form an exact notion of a portion of space so
immense; but some faint idea of it may be obtained from the fact, that,
if the swiftest race-horse ever known had begun to traverse it, at full
speed, at the time of the birth of Moses, he would only as yet have
accomplished half his journey.
It has long been concluded amongst astronomers, that the stars, though
they only appear to our eyes as brilliant points, are all to be
considered as suns, representing so many solar systems, each bearing a
general resemblance to our own. The stars have a brilliancy and apparent
magnitude which we may safely presume to be in proportion to their actual
size and the distance at which they are placed from us. Attempts have
been made to ascertain the distance of some of the stars by calculations
founded on parallax, it being previously understood that, if a parallax
of so much as one second, or the 3600th of a degree, could be ascertained
in any one instance, the distance might be assumed in that instance as
not less than 19,200 millions of miles! In the case of the most
brilliant star, Sirius, even this minute parallax could not be found;
from which of course it was to be inferred that the distance of that star
is something beyond the vast distance which has been stated. In some
others, on which the experiment has been tried, no sensible parallax
could be detected; from which the same inference was to be made in their
case. But a sensible parallax of about one second has been ascertained
in the case of the double star, α α, of the constellation of the Centaur,
{3} and one of the third of that amount for the double star, 61 Cygni;
which gave reason to presume that the distance of the former might be
about twenty thousand millions of miles, and the latter of much greater
amount. If we suppose that similar intervals exist between all the
stars, we shall readily see that the space occupied by even the
comparatively small number visible to the naked eye, must be vast beyond
all powers of conception.
The number visible to the eye is about three thousand; but when a
telescope of small power is directed to the heavens, a great number more
come into view, and the number is ever increased in proportion to the
increased power of the instrument. In one place, where they are more
thickly sown than elsewhere, Sir William Herschel reckoned that fifty
thousand passed over a field of view two degrees in breadth in a single
hour. It was first surmised by the ancient philosopher, Democritus, that
the faintly white zone which spans the sky under the name of the Milky
Way, might be only a dense collection of stars too remote to be
distinguished. This conjecture has been verified by the instruments of
modern astronomers, and some speculations of a most remarkable kind have
been formed in connexion with it. By the joint labours of the two
Herschels, the sky has been “gauged” in all directions by the telescope,
so as to ascertain the conditions of different parts with respect to the
frequency of the stars. The result has been a conviction that, as the
planets are parts of solar systems, so are solar systems parts of what
may be called astral systems—that is, systems composed of a multitude of
stars, bearing a certain relation to each other. The astral system to
which we belong, is conceived to be of an oblong, flattish form, with a
space wholly or comparatively vacant in the centre, while the extremity
in one direction parts into two. The stars are most thickly sown in the
outer parts of this vast ring, and these constitute the Milky Way. Our
sun is believed to be placed in the southern portion of the ring, near
its inner edge, so that we are presented with many more stars, and see
the Milky Way much more clearly, in that direction, than towards the
north, in which line our eye has to traverse the vacant central space.
Nor is this all. Sir William Herschel, so early as 1783, detected a
motion in our solar system with respect to the stars, and announced that
it was tending towards the star λ, in the constellation Hercules. This
has been generally verified by recent and more exact calculations, {5}
which fix on a point in Hercules, near the star 143 of the 17th hour,
according to Piozzi’s catalogue, as that towards which our sun is
proceeding. It is, therefore, receding from the inner edge of the ring.
Motions of this kind, through such vast regions of space, must be long in
producing any change sensible to the inhabitants of our planet, and it is
not easy to grasp their general character; but grounds have nevertheless
been found for supposing that not only our sun, but the other suns of the
system pursue a wavy course round the ring _from west to east_, crossing
and recrossing the middle of the annular circle. “Some stars will depart
more, others less, from either side of the circumference of equilibrium,
according to the places in which they are situated, and according to the
direction and the velocity with which they are put in motion. Our sun is
probably one of those which depart furthest from it, and descend furthest
into the empty space within the ring.” {6} According to this view, a
time may come when we shall be much more in the thick of the stars of our
astral system than we are now, and have of course much more brilliant
nocturnal skies; but it may be countless ages before the eyes which are
to see this added resplendence shall exist.
The evidence of the existence of other astral systems besides our own is
much more decided than might be expected, when we consider that the
nearest of them must needs be placed at a mighty interval beyond our own.
The elder Herschel, directing his wonderful tube towards the _sides_ of
our system, where stars are planted most rarely, and raising the powers
of the instrument to the required pitch, was enabled with awe-struck mind
to see suspended in the vast empyrean astral systems, or, as he called
them, firmaments, resembling our own. Like light cloudlets to a certain
power of the telescope, they resolved themselves, under a greater power,
into stars, though these generally seemed no larger than the finest
particles of diamond dust. The general forms of these systems are
various; but one at least has been detected as bearing a striking
resemblance to the supposed form of our own. The distances are also
various, as proved by the different degrees of telescopic power necessary
to bring them into view. The farthest observed by the astronomer were
estimated by him as thirty-five thousand times more remote than Sirius,
supposing its distance to be about twenty thousand millions of miles. It
would thus appear, that not only does gravitation keep our earth in its
place in the solar system, and the solar system in its place in our
astral system, but it also may be presumed to have the mightier duty of
preserving a local arrangement between that astral system and an
immensity of others, through which the imagination is left to wander on
and on without limit or stay, save that which is given by its inability
to grasp the unbounded.
The two Herschels have in succession made some other most remarkable
observations on the regions of space. They have found within the limits
of our astral system, and generally in its outer fields, a great number
of objects which, from their foggy appearance, are called _nebulæ_; some
of vast extent and irregular figure, as that in the sword of Orion, which
is visible to the naked eye; others of shape more defined; others, again,
in which small bright nuclei appear here and there over the surface.
Between this last form and another class of objects, which appear as
clusters of nuclei with nebulous matter around each nucleus, there is but
a step in what appears a chain of related things. Then, again, our
astral space shews what are called nebulous stars,—namely, luminous
spherical objects, bright in the centre and dull towards the extremities.
These appear to be only an advanced condition of the class of objects
above described. Finally, nebulous stars exist in every stage of
concentration, down to that state in which we see only a common star with
a slight _bur_ around it. It may be presumed that all these are but
stages in a progress, just as if, seeing a child, a boy, a youth, a
middle-aged, and an old man together, we might presume that the whole
were only variations of one being. Are we to suppose that we have got a
glimpse of the process through which a sun goes between its original
condition, as a mass of diffused nebulous matter, and its full-formed
state as a compact body? We shall see how far such an idea is supported
by other things known with regard to the occupants of space, and the laws
of matter.
A superficial view of the astronomy of the solar system gives us only the
idea of a vast luminous body (the sun) in the centre, and a few smaller,
though various sized bodies, revolving at different distances around it;
some of these, again, having smaller planets (satellites) revolving
around them. There are, however, some general features of the solar
system, which, when a profounder attention makes us acquainted with them,
strike the mind very forcibly.
It is, in the first place, remarkable, that the planets all move nearly
_in one plane_, corresponding with the centre of the sun’s body. Next,
it is not less remarkable that the motion of the sun on its axis, those
of the planets around the sun, and the satellites around their primaries,
{9} and the motions of all on their axes, are _in one direction_—namely,
from west to east. Had all these matters been left to accident, the
chances against the uniformity which we find would have been, though
calculable, inconceivably great. Laplace states them at four millions of
millions to one. It is thus powerfully impressed on us, that the
uniformity of the motions, as well as their general adjustment to one
plane, must have been a consequence of some cause acting throughout the
whole system.
Some of the other relations of the bodies are not less remarkable. The
primary planets shew a progressive increase of bulk and diminution of
density, from the one nearest to the sun to that which is most distant.
With respect to density alone, we find, taking water as a measure and
counting it as one, that Saturn is 13/32, or less than half; Jupiter, 1
1/24; Mars, 3 2/7; Earth, 4 1/2; Venus, 5 11/15; Mercury 9 9/10, or about
the weight of lead. Then the distances are curiously relative. It has
been found that if we place the following line of numbers,—
0 3 6 12 24 48 96 192,
and add 4 to each, we shall have a series denoting the respective
distances of the planets from the sun. It will stand thus—
4 7 10 16 28 52 100 196
Merc. Venus. Earth. Mars. Jupiter. Saturn. Uranus.
It will be observed that the first row of figures goes on from the second
on the left hand in a succession of duplications, or multiplications by
2. Surely there is here a most surprising proof of the unity which I am
claiming for the solar system. It was remarked when this curious
relation was first detected, that there was a want of a planet
corresponding to 28; the difficulty was afterwards considered as in a
great measure overcome, by the discovery of four small planets revolving
at nearly one mean distance from the sun, between Mars and Jupiter. The
distances bear an equally interesting mathematical relation to the times
of the revolutions round the sun. It has been found that, with respect
to any two planets, the squares of the times of revolution are to each
other in the same proportion as the cubes of their mean distances,—a most
surprising result, for the discovery of which the world was indebted to
the illustrious Kepler. Sir John Herschel truly observes—“When we
contemplate the constituents of the planetary system from the point of
view which this relation affords us, it is no longer mere analogy which
strikes us, no longer a general resemblance among them, as individuals
independent of each other, and circulating about the sun, each according
to its own peculiar nature, and connected with it by its own peculiar
tie. The resemblance is now perceived to be a true _family likeness_;
they are bound up in one chain—interwoven in one web of mutual relation
and harmonious agreement, subjected to one pervading influence which
extends from the centre to the farthest limits of that great system, of
which all of them, the Earth included, must henceforth be regarded as
members.” {12}
Connecting what has been observed of the series of nebulous stars with
this wonderful relationship seen to exist among the constituents of our
system, and further taking advantage of the light afforded by the
ascertained laws of matter, modern astronomers have suggested the
following hypothesis of the formation of that system.
Of nebulous matter in its original state we know too little to enable us
to suggest how nuclei should be established in it. But, supposing that,
from a peculiarity in its constitution, nuclei are formed, we know very
well how, by virtue of the law of gravitation, the process of an
aggregation of the neighbouring matter to those nuclei should proceed,
until masses more or less solid should become detached from the rest. It
is a well-known law in physics that, when fluid matter collects towards
or meets in a centre, it establishes a rotatory motion. See minor
results of this law in the whirlwind and the whirlpool—nay, on so humble
a scale as the water sinking through the aperture of a funnel. It thus
becomes certain that when we arrive at the stage of a nebulous star, we
have a rotation on an axis commenced.
Now, mechanical philosophy informs us that, the instant a mass begins to
rotate, there is generated a tendency to fling off its outer portions—in
other words, the law of centrifugal force begins to operate. There are,
then, two forces acting in opposition to each other, the one attracting
_to_, the other throwing _from_, the centre. While these remain exactly
counterpoised, the mass necessarily continues entire; but the least
excess of the centrifugal over the attractive force would be attended
with the effect of separating the mass and its outer parts. These outer
parts would, then, be left as a ring round the central body, which ring
would continue to revolve with the velocity possessed by the central mass
at the moment of separation, but not necessarily participating in any
changes afterwards undergone by that body. This is a process which might
be repeated as soon as a new excess arose in the centrifugal over the
attractive forces working in the parent mass. It might, indeed, continue
to be repeated, until the mass attained the ultimate limits of the
condensation which its constitution imposed upon it. From what cause
might arise the periodical occurrence of an excess of the centrifugal
force? If we suppose the agglomeration of a nebulous mass to be a
process attended by refrigeration or cooling, which many facts render
likely, we can easily understand why the outer parts, hardening under
this process, might, by virtue of the greater solidity thence acquired,
begin to present some resistance to the attractive force. As the
solidification proceeded, this resistance would become greater, though
there would still be a tendency to adhere. Meanwhile, the condensation
of the central mass would be going on, tending to produce a separation
from what may now be termed the _solidifying crust_. During the
contention between the attractions of these two bodies, or parts of one
body, there would probably be a ring of attenuation between the mass and
its crust. At length, when the central mass had reached a certain stage
in its advance towards solidification, a separation would take place, and
the crust would become a detached ring. It is clear, of course, that
some law presiding over the refrigeration of heated gaseous bodies would
determine the stages at which rings were thus formed and detached. We do
not know any such law, but what we have seen assures us it is one
observing and reducible to mathematical formulæ.
If these rings consisted of matter nearly uniform throughout, they would
probably continue each in its original form; but there are many chances
against their being uniform in constitution. The unavoidable effects of
irregularity in their constitution would be to cause them to gather
towards centres of superior solidity, by which the annular form would, of
course, be destroyed. The ring would, in short, break into several
masses, the largest of which would be likely to attract the lesser into
itself. The whole mass would then necessarily settle into a spherical
form by virtue of the law of gravitation; in short, would then become a
planet revolving round the sun. Its rotatory motion would, of course,
continue, and satellites might then be thrown off in turn from its body
in exactly the same way as the primary planets had been thrown off from
the sun. The rule, if I can be allowed so to call it, receives a
striking support from what appear to be its exceptions. While there are
many chances against the matter of the rings being sufficiently equable
to remain in the annular form till they were consolidated, it might
nevertheless be otherwise in some instances; that is to say, the
equableness might, in those instances, be sufficiently great. Such was
probably the case with the two rings around the body of Saturn, which
remain a living picture of the arrangement, if not the condition, in
which all the planetary masses at one time stood. It may also be
admitted that, when a ring broke up, it was possible that the fragments
might spherify separately. Such seems to be the actual history of the
ring between Jupiter and Mars, in whose place we now find four planets
much beneath the smallest of the rest in size, and moving nearly at the
same distance from the sun, though in orbits so elliptical, and of such
different planes, that they keep apart.
It has been seen that there are mathematical proportions in the relative
distances and revolutions of the planets of our system. It has also been
suggested that the periods in the condensation of the nebulous mass, at
which rings were disengaged, must have depended on some particular crises
in the condition of that mass, in connexion with the laws of centrifugal
force and attraction. M. Compte, of Paris, has made some approach to the
verification of the hypothesis, by calculating what ought to have been
the rotation of the solar mass at the successive times when its surface
extended to the various planetary orbits. He ascertained that _that
rotation corresponded in every case with the actual sidereal revolution
of the planets_, _and that the rotation of the primary planets in like
manner corresponded with the orbitual periods of the secondaries_. The
process by which he arrived at this conclusion is not to be readily
comprehended by the unlearned; but those who are otherwise, allow that it
is a powerful support to the present hypothesis of the formation of the
globes of space. {17}
The nebular hypothesis, as it has been called, obtains a remarkable
support in what would at first seem to militate against it—the existence
in our firmament of several thousands of solar systems, in which there
are more than one sun. These are called double and triple stars. Some
double stars, upon which careful observations have been made, are found
to have a regular revolutionary motion round each other in ellipses.
This kind of solar system has also been observed in what appears to be
its rudimental state, for there are examples of nebulous stars containing
two and three nuclei in near association. At a certain point in the
confluence of the matter of these nebulous stars, they would all become
involved in a common revolutionary motion, linked inextricably with each
other, though it might be at sufficient distances to allow of each
distinct centre having afterwards its attendant planets. We have seen
that the law which causes rotation in the single solar masses, is exactly
the same which produces the familiar phenomenon of a small whirlpool or
dimple in the surface of a stream. Such dimples are not always single.
Upon the face of a river where there are various contending currents, it
may often be observed that two or more dimples are formed near each other
with more or less regularity. These fantastic eddies, which the musing
poet will sometimes watch abstractedly for an hour, little thinking of
the law which produces and connects them, are an illustration of the
wonders of binary and ternary solar systems.
The nebular hypothesis is, indeed, supported by so many ascertained
features of the celestial scenery, and by so many calculations of exact
science, that it is impossible for a candid mind to refrain from giving
it a cordial reception, if not to repose full reliance upon it, even
without seeking for it support of any other kind. Some other support I
trust yet to bring to it; but in the meantime, assuming its truth, let us
see what idea it gives of the constitution of what we term the universe,
of the development of its various parts, and of its original condition.
Reverting to a former illustration—if we could suppose a number of
persons of various ages presented to the inspection of an intelligent
being newly introduced into the world, we cannot doubt that he would soon
become convinced that men had once been boys, that boys had once been
infants, and, finally, that all had been brought into the world in
exactly the same circumstances. Precisely thus, seeing in our astral
system many thousands of worlds in all stages of formation, from the most
rudimental to that immediately preceding the present condition of those
we deem perfect, it is unavoidable to conclude that all the perfect have
gone through the various stages which we see in the rudimental. This
leads us at once to the conclusion that the whole of our firmament was at
one time a diffused mass of nebulous matter, extending through the space
which it still occupies. So also, of course, must have been the other
astral systems. Indeed, we must presume the whole to have been
originally in one connected mass, the astral systems being only the first
division into parts, and solar systems the second.
The first idea which all this impresses upon us is, that the formation of
bodies in space is _still and at present in progress_. We live at a time
when many have been formed, and many are still forming. Our own solar
system is to be regarded as completed, supposing its perfection to
consist in the formation of a series of planets, for there are
mathematical reasons for concluding that Mercury is the nearest planet to
the sun, which can, according to the laws of the system, exist. But
there are other solar systems within our astral system, which are as yet
in a less advanced state, and even some quantities of nebulous matter
which have scarcely begun to advance towards the stellar form. On the
other hand, there are vast numbers of stars which have all the appearance
of being fully formed systems, if we are to judge from the complete and
definite appearance which they present to our vision through the
telescope. We have no means of judging of the seniority of systems; but
it is reasonable to suppose that, among the many, some are older than
ours. There is, indeed, one piece of evidence for the probability of the
comparative youth of our system, altogether apart from human traditions
and the geognostic appearances of the surface of our planet. This
consists in a thin nebulous matter, which is diffused around the sun to
nearly the orbit of Mercury, of a very oblately spheroidal shape. This
matter, which sometimes appears to our naked eyes, at sunset, in the form
of a cone projecting upwards in the line of the sun’s path, and which
bears the name of the Zodiacal Light, has been thought a residuum or last
remnant of the concentrating matter of our system, and thus may be
supposed to indicate the comparative recentness of the principal events
of our cosmogony. Supposing the surmise and inference to be correct, and
they may be held as so far supported by more familiar evidence, we might
with the more confidence speak of our system as not amongst the elder
born of Heaven, but one whose various phenomena, physical and moral, as
yet lay undeveloped, while myriads of others were fully fashioned and in
complete arrangement. Thus, in the sublime chronology to which we are
directing our inquiries, we first find ourselves called upon to consider
the globe which we inhabit as a child of the sun, elder than Venus and
her younger brother Mercury, but posterior in date of birth to Mars,
Jupiter, Saturn, and Uranus; next to regard our whole system as probably
of recent formation in comparison with many of the stars of our
firmament. We must, however, be on our guard against supposing the earth
as a recent globe in our ordinary conceptions of time. From evidence
afterwards to be adduced, it will be seen that it cannot be presumed to
be less than many hundreds of centuries old. How much older Uranus may
be no one can tell, much less how more aged may be many of the stars of
our firmament, or the stars of other firmaments than ours.
Another and more important consideration arises from the hypothesis;
namely, as to the means by which the grand process is conducted. The
nebulous matter collects around nuclei by virtue of the law of
attraction. The agglomeration brings into operation another physical
law, by force of which the separate masses of matter are either made to
rotate singly, or, in addition to that single motion, are set into a
coupled revolution in ellipses. Next centrifugal force comes into play,
flinging off portions of the rotating masses, which become spheres by
virtue of the same law of attraction, and are held in orbits of
revolution round the central body by means of a composition between the
centrifugal and gravitating forces. All, we see, is done by certain laws
of matter, so that it becomes a question of extreme interest, what are
such laws? All that can yet be said, in answer, is, that we see certain
natural events proceeding in an invariable order under certain
conditions, and thence infer the existence of some fundamental
arrangement which, for the bringing about of these events, has a force
and certainty of action similar to, but more precise and unerring than
those arrangements which human society makes for its own benefit, and
calls laws. It is remarkable of physical laws, that we see them
operating on every kind of scale as to magnitude, with the same
regularity and perseverance. The tear that falls from childhood’s cheek
is globular, through the efficacy of that same law of mutual attraction
of particles which made the sun and planets round. The rapidity of
Mercury is quicker than that of Saturn, for the same reason that, when we
wheel a ball round by a string and make the string wind up round our
fingers, the ball always flies quicker and quicker as the string is
shortened. Two eddies in a stream, as has been stated, fall into a
mutual revolution at the distance of a couple of inches, through the same
cause which makes a pair of suns link in mutual revolution at the
distance of millions of miles. There is, we might say, a sublime
simplicity in this indifference of the grand regulations to the vastness
or minuteness of the field of their operation. Their being uniform, too,
throughout space, as far as we can scan it, and their being so unfailing
in their tendency to operate, so that only the proper conditions are
presented, afford to our minds matter for the gravest consideration. Nor
should it escape our careful notice that the regulations on which all the
laws of matter operate, are established on a rigidly accurate
mathematical basis. Proportions of numbers and geometrical figures rest
at the bottom of the whole. All these considerations, when the mind is
thoroughly prepared for them, tend to raise our ideas with respect to the
character of physical laws, even though we do not go a single step
further in the investigation. But it is impossible for an intelligent
mind to stop there. We advance from law to the cause of law, and ask,
What is that? Whence have come all these beautiful regulations? Here
science leaves us, but only to conclude, from other grounds, that there
is a First Cause to which all others are secondary and ministrative, a
primitive almighty will, of which these laws are merely the mandates.
That great Being, who shall say where is his dwelling-place, or what his
history! Man pauses breathless at the contemplation of a subject so much
above his finite faculties, and only can wonder and adore!
CONSTITUENT MATERIALS OF THE EARTH
AND OF THE OTHER BODIES OF SPACE.
THE nebular hypothesis almost necessarily supposes matter to have
originally formed one mass. We have seen that the same physical laws
preside over the whole. Are we also to presume that the constitution of
the whole was uniform?—that is to say, that the whole consisted of
similar elements. It seems difficult to avoid coming to this conclusion,
at least under the qualification that, possibly, various bodies, under
peculiar circumstances attending their formation, may contain elements
which are wanting, and lack some which are present in others, or that
some may entirely consist of elements in which others are entirely
deficient.
What are elements? This is a term applied by the chemist to a certain
limited number of substances, (fifty-four or fifty-five are ascertained,)
which, in their combinations, form all the matters of every kind present
in and about our globe. They are called elements, or simple substances,
because it has hitherto been found impossible to reduce them into others,
wherefore they are presumed to be the primary bases of all matters. It
has, indeed, been surmised that these so-called elements are only
modifications of a primordial form of matter, brought about under certain
conditions; but if this should prove to be the case, it would little
affect the view which we are taking of cosmical arrangements. Analogy
would lead us to conclude that the combinations of the primordial matter,
forming our so-called elements, are as universal or as liable to take
place everywhere as are the laws of gravitation and centrifugal force.
We must therefore presume that the gases, the metals, the earths, and
other simple substances, (besides whatever more of which we have no
acquaintance,) exist or are liable to come into existence under proper
conditions, as well in the astral system, which is thirty-five thousand
times more distant than Sirius, as within the bounds of our own solar
system or our own globe.
Matter, whether it consist of about fifty-five ingredients, or only one,
is liable to infinite varieties of condition under different
circumstances, or, to speak more philosophically, under different laws.
As a familiar illustration, water, when subjected to a temperature under
32° Fahrenheit, becomes ice; raise the temperature to 212°, and it
becomes steam, occupying a vast deal more space than it formerly did.
The gases, when subjected to pressure, become liquids; for example,
carbonic acid gas, when subjected to a weight equal to a column of water
1230 feet high, at a temperature of 32°, takes this form: the other gases
require various amounts of pressure for this transformation, but all
appear to be liable to it when the pressure proper in each case is
administered. Heat is a power greatly concerned in regulating the volume
and other conditions of matter. A chemist can reckon with considerable
precision what additional amount of heat would be required to vaporise
all the water of our globe; how much more to disengage the oxygen which
is diffused in nearly a proportion of one-half throughout its solids;
and, finally, how much more would be required to cause the whole to
become vaporiform, which we may consider as equivalent to its being
restored to its original nebulous state. He can calculate with equal
certainty what would be the effect of a considerable diminution of the
earth’s temperature—what changes would take place in each of its
component substances, and how much the whole would shrink in bulk.
The earth and all its various substances have at present a certain volume
in consequence of the temperature which actually exists. When, then, we
find that its matter and that of the associate planets was at one time
diffused throughout the whole space, now circumscribed by the orbit of
Uranus, we cannot doubt, after what we know of the power of heat, that
the nebulous form of matter was attended by the condition of a very high
temperature. The nebulous matter of space, previously to the formation
of stellar and planetary bodies, must have been a universal Fire Mist, an
idea which we can scarcely comprehend, though the reasons for arriving at
it seem irresistible. The formation of systems out of this matter
implies a change of some kind with regard to the condition of the heat.
Had this power continued to act with its full original repulsive energy,
the process of agglomeration by attraction could not have gone on. We do
not know enough of the laws of heat to enable us to surmise how the
necessary change in this respect was brought about, but we can trace some
of the steps and consequences of the process. Uranus would be formed at
the time when the heat of our system’s matter was at the greatest, Saturn
at the next, and so on. Now this tallies perfectly with the exceeding
diffuseness of the matter of those elder planets, Saturn being not more
dense or heavy than the substance cork. It may be that a sufficiency of
heat still remains in those planets to make up for their distance from
the sun, and the consequent smallness of the heat which they derive from
his rays. And it may equally be, since Mercury is twice the density of
the earth, that its matter exists under a degree of cold for which that
planet’s large enjoyment of the sun’s rays is no more than a
compensation. Thus there may be upon the whole a nearly equal experience
of heat amongst all these children of the sun. Where, meanwhile, is the
heat once diffused through the system over and above what remains in the
planets? May we not rationally presume it to have gone to constitute
that luminous envelope of the sun, in which his warmth-giving power is
now held to reside? It could not be destroyed—it cannot be supposed to
have gone off into space—it must have simply been reserved to constitute,
at the last, a means of sustaining the many operations of which the
planets were destined to be the theatre.
The tendency of the whole of the preceding considerations is to bring the
conviction that our globe is a specimen of all the similarly-placed
bodies of space, as respects its constituent matter and the physical and
chemical laws governing it, with only this qualification, that there are
_possibly_ shades of variation with respect to the component materials,
and _undoubtedly_ with respect to the conditions under which the laws
operate, and consequently the effects which they produce. Thus, there
may be substances here which are not in some other bodies, and substances
here solid may be elsewhere liquid or vaporiform. We are the more
entitled to draw such conclusions, seeing that there is nothing at all
singular or special in the astronomical situation of the earth. It takes
its place third in a series of planets, which series is only one of
numberless other systems forming one group. It is strikingly—if I may
use such an expression—a member of a democracy. Hence, we cannot suppose
that there is any peculiarity about it which does not probably attach to
multitudes of other bodies—in fact, to all that are analogous to it in
respect of cosmical arrangements.
It therefore becomes a point of great interest—what are the materials of
this specimen? What is the constitutional character of this object,
which may be said to be a sample, presented to our immediate observation,
of those crowds of worlds which seem to us as the particles of the desert
sand-cloud in number, and to whose profusion there are no conceivable
local limits?
The solids, liquids, and aeriform fluids of our globe are all, as has
been stated, reducible into fifty-five substances hitherto called
elementary. Six are gases; oxygen, hydrogen, and nitrogen being the
chief. Forty-two are metals, of which eleven are remarkable as
composing, in combination with oxygen, certain earths, as magnesia, lime,
alumin. The remaining six, including carbon, silicon, sulphur, have not
any general appellation.
The gas oxygen is considered as by far the most abundant substance in our
globe. It constitutes a fifth part of our atmosphere, a third part of
water, and a large proportion of every kind of rock in the crust of the
earth. Hydrogen, which forms two-thirds of water, and enters into some
mineral substances, is perhaps next. Nitrogen, of which the atmosphere
is four-fifths composed, must be considered as an abundant substance.
The metal silicium, which unites with oxygen in nearly equal parts to
form silica, the basis of nearly a half of the rocks in the earth’s
crust, is, of course, an important ingredient. Aluminium, the metallic
basis of alumin, a large material in many rocks, is another abundant
elementary substance. So, also, is carbon a small ingredient in the
atmosphere, but the chief constituent of animal and vegetable substances,
and of all fossils which ever were in the latter condition, amongst which
coal takes a conspicuous place. The familiarly-known metals, as iron,
tin, lead, silver, gold, are elements of comparatively small magnitude in
that exterior part of the earth’s body which we are able to investigate.
It is remarkable of the simple substances that they are generally in some
compound form. Thus, oxygen and nitrogen, though in union they form the
aerial envelope of the globe, are never found separate in nature. Carbon
is pure only in the diamond. And the metallic bases of the earths,
though the chemist can disengage them, may well be supposed unlikely to
remain long uncombined, seeing that contact with moisture makes them
burn. Combination and re-combination are principles largely pervading
nature. There are few rocks, for example, that are not composed of at
least two varieties of matter, each of which is again a compound of
elementary substances. What is still more wonderful with respect to this
principle of combination, all the elementary substances observe certain
mathematical proportions in their unions. One volume of them unites with
one, two, three, or more volumes of another, any extra quantity being
sure to be left over, if such there should be. It is hence supposed that
matter is composed of infinitely minute particles or atoms, each of which
belonging to any one substance, can only (through the operation of some
as yet hidden law) associate with a certain number of the atoms of any
other. There are also strange predilections amongst substances for each
other’s company. One will remain combined in solution with another, till
a third is added, when it will abandon the former and attach itself to
the latter. A fourth being added, the third will perhaps leave the
first, and join the new comer.
Such is an outline of the information which chemistry gives us regarding
the constituent materials of our globe. How infinitely is the knowledge
increased in interest, when we consider the probability of such being the
materials of the whole of the bodies of space, and the laws under which
these everywhere combine, subject only to local and accidental
variations!
In considering the cosmogenic arrangements of our globe, our attention is
called in a special degree to the moon.
In the nebular hypothesis, satellites are considered as masses thrown off
from their primaries, exactly as the primaries had previously been from
the sun. The orbit of any satellite is also to be regarded as marking
the bounds of the mass of the primary at the time when that satellite was
thrown off; its speed likewise denotes the rapidity of the rotatory
motion of the primary at that particular juncture. For example, the
outermost of the four satellites of Jupiter revolves round his body at
the distance of 1,180,582 miles, shewing that the planet was once
3,675,501 miles in circumference, instead of being, as now, only 89,170
miles in diameter. This large mass took rather more than sixteen days
six hours and a half (the present revolutionary period of the outermost
satellite) to rotate on its axis. The innermost satellite must have been
formed when the planet was reduced to a circumference of 309,075 miles,
and rotated in about forty-two hours and a half.
From similar inferences, we find that the mass of the earth, at a certain
point of time after it was thrown off from the sun, was no less than
482,000 miles in diameter, being sixty times what it has since shrunk to.
At that time, the mass must have taken rather more than twenty-nine and a
half days to rotate, (being the revolutionary period of the moon,)
instead of as now, rather less than twenty-four hours.
The time intervening between the formation of the moon and the earth’s
diminution to its present size, was probably one of those vast sums in
which astronomy deals so largely, but which the mind altogether fails to
grasp.
The observations made upon the surface of the moon by telescopes, tend
strongly to support the hypothesis as to all the bodies of space being
composed of similar matters, subject to certain variations. It does not
appear that our satellite is provided with that gaseous envelope which,
on earth, performs so many important functions. Neither is there any
appearance of water upon the surface; yet that surface is, like that of
our globe, marked by inequalities and the appearance of volcanic
operations. These inequalities and volcanic operations are upon a scale
far greater than any which now exist upon the earth’s surface. Although,
from the greater force of gravitation upon its exterior, the mountains,
other circumstances being equal, might have been expected to be much
smaller than ours, they are, in many instances, equal in height to nearly
the highest of our Andes. They are generally of extreme steepness, and
sharp of outline, a peculiarity which might be looked for in a planet
deficient in water and atmosphere, seeing that these are the agents which
wear down ruggedness on the surface of our earth. The volcanic
operations are on a stupendous scale. They are the cause of the bright
spots of the moon, while the want of them is what distinguishes the
duller portions, usually but erroneously called _seas_. In some parts,
bright volcanic matter, besides covering one large patch, radiates out in
long streams, which appear studded with subordinate _foci_ of the same
kind of energy. Other objects of a most remarkable character are ring
mountains, mounts like those of the craters of earthly volcanoes,
surrounded immediately by vast and profound circular pits, hollowed under
the general surface, these again being surrounded by a circular wall of
mountain, rising far above the central one, and in the inside of which
are terraces about the same height as the inner eminence. The well-known
bright spot in the south-east quarter, called by astronomers _Tycho_, and
which can be readily distinguished by the naked eye, is one of these
ring-mountains. There is one of 200 miles in diameter, with a pit 22,000
feet deep; that is, twice the height of Ætna. It is remarkable, that the
maps given by Humboldt of a volcanic district in South America, and one
illustrative of the formerly volcanic district of Auvergne, in France,
present features strikingly like many parts of the moon’s surface, as
seen through a good glass.
These characteristics of the moon forbid the idea that it can be at
present a theatre of life like the earth, and almost seem to declare that
it never can become so. But we must not rashly draw any such
conclusions. The moon may be only in an earlier stage of the progress
through which the earth has already gone. The elements which seem
wanting may be only in combinations different in those which exist here,
and may yet be developed as we here find them. Seas may yet fill the
profound hollows of the surface; an atmosphere may spread over the whole.
Should these events take place, meteorological phenomena, and all the
phenomena of organic life, will commence, and the moon, like the earth,
will become a green and inhabited world.
It is unavoidably held as a strong proof in favour of any hypothesis,
when all the relative phenomena are in harmony with it. This is
eminently the case with the nebulous hypothesis, for here the associated
facts cannot be explained on any other supposition. We have seen reason
to conclude that the primary condition of matter was that of a diffused
mass, in which the component molecules were probably kept apart through
the efficacy of heat; that portions of this agglomerated into suns, which
threw off planets; that these planets were at first very much diffused,
but gradually contracted by cooling to their present dimensions. Now, as
to our own globe, there is a remarkable proof of its having been in a
fluid state at the time when it was finally solidifying, in the fact of
its being bulged at the equator, the very form which a soft revolving
body takes, and must inevitably take, under the influence of centrifugal
force. This bulging makes the equatorial exceed the polar diameter as
230 to 229, which has been demonstrated to be precisely the departure
from a correct sphere which might be predicated from a knowledge of the
amount of the mass and the rate of rotation. There is an almost equally
distinct memorial of the original high temperature of the materials, in
the store of heat which still exists in the interior. The immediate
surface of the earth, be it observed, exhibits only the temperature which
might be expected to be imparted to such materials, by the heat of the
sun. There is a point, very short way down, but varying in different
climes, where all effect from the sun’s rays ceases. Then, however,
commences a temperature from an entirely different cause, one which
evidently has its source in the interior of the earth, and which
regularly increases as we descend to greater and greater depths, the rate
of increment being about one degree Fahrenheit for every sixty feet; and
of this high temperature there are other evidences, in the phenomena of
volcanoes and thermal springs, as well as in what is ascertained with
regard to the density of the entire mass of the earth. This, it will be
remembered, is four and a half times the weight of water; but the actual
weight of the principal solid substances composing the outer crust is as
two and a half times the weight of water; and this, we know, if the globe
were solid and cold, should increase vastly towards the centre, water
acquiring the density of quicksilver at 362 miles below the surface, and
other things in proportion, and these densities becoming much greater at
greater depths; so that the entire mass of a cool globe should be of a
gravity infinitely exceeding four and a half times the weight of water.
The only alternative supposition is, that the central materials are
greatly expanded or diffused by some means; and by what means could they
be so expanded but by heat? Indeed, the existence of this central heat,
a residuum of that which kept all matter in a vaporiform chaos at first,
is amongst the most solid discoveries of modern science, {42} and the
support which it gives to Herschel’s explanation of the formation of
worlds is most important. We shall hereafter see what appear to be
traces of an operation of this heat upon the surface of the earth in very
remote times; an effect, however, which has long passed entirely away.
The central heat has, for ages, reached a fixed point, at which it will
probably remain for ever, as the non-conducting quality of the cool crust
absolutely prevents it from suffering any diminution.
THE EARTH FORMED—ERA OF THE
PRIMARY ROCKS.
ALTHOUGH the earth has not been actually penetrated to a greater depth
than three thousand feet, the nature of its substance can, in many
instances, be inferred for the depth of many miles by other means of
observation. We see a mountain composed of a particular substance, with
strata, or beds of other rock, lying against its sloped sides; we, of
course, infer that the substance of the mountain dips away under the
strata which we see lying against it. Suppose that we walk away from the
mountain across the turned up edges of the stratified rocks, and that for
many miles we continue to pass over other stratified rocks, all disposed
in the same way, till by and bye we come to a place where we begin to
cross the opposite edges of the same beds; after which we pass over these
rocks all in reverse order till we come to another extensive mountain
composed of similar material to the first, and shelving away under the
strata in the same way. We should then infer that the stratified rocks
occupied a basin formed by the rock of these two mountains, and by
calculating the thickness right through these strata, could be able to
say to what depth the rock of the mountain extended below. By such
means, the kind of rock existing many miles below the surface can often
be inferred with considerable confidence.
The interior of the globe has now been inspected in this way in many
places, and a tolerably distinct notion of its general arrangements has
consequently been arrived at. It appears that the basis rock of the
earth, as it may be called, is of hard texture, and crystalline in its
constitution. Of this rock, granite may be said to be the type, though
it runs into many varieties. Over this, except in the comparatively few
places where it projects above the general level in mountains, other
rocks are disposed in sheets or strata, with the appearance of having
been deposited originally from water; but these last rocks have nowhere
been allowed to rest in their original arrangement. Uneasy movements
from below have broken them up in great inclined masses, while in many
cases there has been projected through the rents rocky matter more or
less resembling the great inferior crystalline mass. This rocky matter
must have been in a state of fusion from heat at the time of its
projection, for it is often found to have run into and filled up lateral
chinks in these rents. There are even instances where it has been rent
again, and a newer melted matter of the same character sent through the
opening. Finally, in the crust as thus arranged there are, in many
places, chinks containing veins of metal. Thus, there is first a great
inferior mass, composed of crystalline rock, and probably resting
immediately on the fused and expanded matter of the interior: next,
layers or strata of aqueous origin; next, irregular masses of melted
inferior rock that have been sent up volcanically and confusedly at
various times amongst the aqueous rocks, breaking up these into masses,
and tossing them out of their original levels. This is an outline of the
arrangements of the crust of the earth, as far as we can observe it. It
is, at first sight, a most confused scene; but after some careful
observation, we readily detect in it a regularity and order from which
much instruction in the history of our globe is to be derived.
The deposition of the aqueous rocks, and the projection of the volcanic,
have unquestionably taken place since the settlement of the earth in its
present form. They are indeed of an order of events which we see going
on, under the agency of more or less intelligible causes, even down to
the present day. We may therefore consider them generally as
comparatively recent transactions. Abstracting them from the
investigations before us, we arrive at the idea of the earth in its first
condition as a globe of its present size—namely, as a mass, externally at
least, consisting of the crystalline kind of rock, with the waters of the
present seas and the present atmosphere around it, though these were
probably in considerably different conditions, both as to temperature and
their constituent materials, from what they now are. We are thus to
presume that that crystalline texture of rock which we see exemplified in
granite is the condition into which the great bulk of the solids of our
earth were agglomerated directly from the nebulous or vaporiform state.
It is a condition eminently of combination, for such rock is invariably
composed of two or more of four substances—silica, mica, quartz, and
hornblende—which associate in it in the form of grains or crystals, and
which are themselves each composed of a group of the simple or elementary
substances.
Judging from the results and from still remaining conditions, we must
suppose that the heat retained in the interior of the globe was more
intense, or had greater freedom to act, in some places than in others.
These became the scenes of volcanic operations, and in time marked their
situations by the extrusion of traps and basalts from below—namely, rocks
composed of the crystalline matter fused by intense heat, and developed
on the surface in various conditions, according to the particular
circumstances under which it was sent up; some, for example, being thrown
up under water, and some in the open air, which conditions are found to
have made considerable difference in its texture and appearance. The
great stores of subterranean heat also served an important purpose in the
formation of the aqueous rocks. These rocks might, according to Sir John
Herschel, become subject to heat in the following manner:—While the
surface of a particular mass of rock forms the bed of the sea, the heat
is kept at a certain distance from that surface by the contact of the
water; philosophically speaking, it radiates away the heat into the sea,
and (to resort to common language) is cooled a good way down. But when
new sediment settles at the bottom of that sea, the heat rises up to what
was formerly the surface; and when a second quantity of sediment is laid
down, it continues to rise through the first of the deposits, which then
becomes subjected to those changes which heat is calculated to produce.
This process is precisely the same as that of putting additional coats
upon our own bodies; when, of course, the internal heat rises through
each coat in succession, and the third (supposing there is a fourth above
it) becomes as warm as perhaps the first originally was.
In speaking of sedimentary rocks, we may be said to be anticipating. It
is necessary, first, to shew how such rocks were formed, or how
stratification commenced.
Geology tells us as plainly as possible, that the original crystalline
mass was not a perfectly smooth ball, with air and water playing round
it. There were vast irregularities in the surface,—irregularities
trifling, perhaps, compared with the whole bulk of the globe, but
assuredly vast in comparison with any which now exist upon it. These
irregularities might be occasioned by inequalities in the cooling of the
substance, or by accidental and local sluggishness of the materials, or
by local effects of the concentrated internal heat. From whatever cause
they arose, there they were—enormous granitic mountains, interspersed
with seas which sunk to a depth equally profound, and by which, perhaps,
the mountains were wholly or partially covered. Now, it is a fact of
which the very first principles of geology assure us, that the solids of
the globe cannot for a moment be exposed to water, or to the atmosphere,
without becoming liable to change. They instantly begin to wear down.
This operation, we may be assured, proceeded with as much certainty in
the earliest ages of our earth’s history, as it does now, but upon a much
more magnificent scale. There is the clearest evidence that the seas of
those days were not in some instances less than a hundred miles in depth,
however much more. The sub-aqueous mountains must necessarily have been
of at least equal magnitude. The system of disintegration consequent
upon such conditions would be enormous. The matters worn off, being
carried into the neighbouring depths, and there deposited, became the
components of the earliest stratified rocks, the first series of which is
the _Gneiss and Mica Slate System_, or series, examples of which are
exposed to view in the Highlands of Scotland and in the West of England.
The vast thickness of these beds, in some instances, is what attests the
profoundness of the primeval oceans in which they were formed; the
Pensylvanian grawacke, a member of the next highest series, is not less
than a hundred miles in direct thickness. We have also evidence that the
earliest strata were formed in the presence of a stronger degree of heat
than what operated in subsequent stages of the world, for the laminæ of
the gneiss and of the mica and chlorite schists are contorted in a way
which could only be the result of a very high temperature. It appears as
if the seas in which these deposits were formed, had been in the troubled
state of a caldron of water nearly at boiling heat. Such a condition
would probably add not a little to the disintegrating power of the ocean.
The earliest stratified rocks contain no matters which are not to be
found in the primitive granite. They are the same in material, but only
changed into new forms and combinations; hence they have been called by
Mr. Lyell, metamorphic rocks. But how comes it that some of them are
composed almost exclusively of one of the materials of granite; the mica
schists, for example, of mica—the quartz rocks, of quartz, &c.? For this
there are both chemical and mechanical causes. Suppose that a river has
a certain quantity of material to carry down, it is evident that it will
soonest drop the larger particles, and carry the lightest farthest on.
To such a cause is it owing that some of the materials of the worn-down
granite have settled in one place and some in another. {52} Again, some
of these materials must be presumed to have been in a state of chemical
solution in the primeval seas. It would be, of course, in conformity
with chemical laws, that certain of these materials would be precipitated
singly, or in modified combinations, to the bottom, so as to form rocks
by themselves.
The rocks hitherto spoken of contain none of those petrified remains of
vegetables and animals which abound so much in subsequently formed rocks,
and tell so wondrous a tale of the past history of our globe. They
simply contain, as has been said, mineral materials derived from the
primitive mass, and which appear to have been formed into strata in seas
of vast depth. The absence from these rocks of all traces of vegetable
and animal life, joined to a consideration of the excessive temperature
which seems to have prevailed in their epoch, has led to the inference
that no plants or animals of any kind then existed. A few geologists
have indeed endeavoured to shew that the absence of organic remains is no
proof of the globe having been then unfruitful or uninhabited, as the
heat to which these rocks have been subjected at the time of their
solidification, might have obliterated any remains of either plants or
animals which were included in them. But this is only an hypothesis of
negation; and it certainly seems very unlikely that a degree of heat
sufficient to obliterate the remains of plants or animals when dead,
would ever allow of their coming into or continuing in existence.
COMMENCEMENT OF ORGANIC LIFE—
SEA PLANTS, CORALS, ETC.
WE can scarcely be said to have passed out of these rocks, when we begin
to find new conditions in the earth. It is here to be observed that the
subsequent rocks are formed, in a great measure, of matters derived from
the substance of those which went before, but contain also beds of
limestone, which is to no small extent composed of an ingredient which
has not hitherto appeared. Limestone is a carbonate of lime, a secondary
compound, of which one of the ingredients, carbonic acid gas, presents
the element _carbon_, a perfect novelty in our progress. Whence this
substance? The question is the more interesting, from our knowing that
carbon is the main ingredient in organic things. There is reason to
believe that its primeval condition was that of a gas, confined in the
interior of the earth, and diffused in the atmosphere. The atmosphere
still contains about a two-thousandth part of carbonic acid gas, forming
the grand store from which the substance of each year’s crop of herbage
and grain is derived, passing from herbage and grain into animal
substance, and from animals again rendered back to the atmosphere in
their expired breath, so that its amount is never impaired. Knowing
this, when we hear of carbon beginning to appear in the ascending series
of rocks, we are unavoidably led to consider it as marking a time of some
importance in the earth’s history, a new era of natural conditions, one
in which organic life has probably played a part.
It is not easy to suppose that, at this period, carbon was adopted
directly in its gaseous form into rocks; for, if so, why should it not
have been taken into earlier ones also? But we know that plants take it
in, and transform it into substance; and we also know that there are
classes of animals (marine polypes) which are capable of appropriating
it, in connexion with lime, (carbonate of lime,) from the waters of the
ocean, provided it be there in solution; and this substance do these
animals deposit in masses (coral reefs) equal in extent to many strata.
It has even been suggested, on strong grounds of probability, that a
class of limestone beds are simply these reefs subjected to subsequent
heat and pressure.
The appearance, then, of limestone beds in the early part of the
stratified series, may be presumed to be connected with the fact of the
commencement of organic life upon our planet, and, indeed, a consequent
and a symptom of it.
It may not be out of place here to remark, that carbon is presumed to
exist largely in the interior of the earth, from the fact of such
considerable quantities of it issuing at this day, in the form of
carbonic acid gas, from fissures and springs. The primeval and
subsequent history of this element is worthy of much attention, and we
shall have to revert to it as a matter greatly concerning our subject.
Delabeche estimates the quantity of carbonic acid gas locked up in every
cubic yard of limestone, at 16,000 cubic feet. The quantity locked up in
coal, in which it forms from 64 to 75 per cent., must also be enormous.
If all this were disengaged in a gaseous form, the constitution of the
atmosphere would undergo a change, of which the first effect would be the
extinction of life in all land animals. But a large proportion of it
must have at one time been in the atmosphere. The atmosphere would then,
of course, be incapable of supporting life in land animals. It is
important, however, to observe that such an atmosphere would not be
inconsistent with a luxuriant land vegetation; for experiment has proved
that plants will flourish in air containing _one-twelfth_ of this gas, or
166 times more than the present charge of our atmosphere. The results
which we observe are perfectly consistent with, and may be said to
presuppose an atmosphere highly charged with this gas, from about the
close of the primary non-fossiliferous rocks to the termination of the
carboniferous series, for there we see vast deposits (coal) containing
carbon as a large ingredient, while at the same time the leaves of the
_Stone Book_ present no record of the contemporaneous existence of land
animals.
The hypothesis of the connexion of the first limestone beds with the
commencement of organic life upon our planet is supported by the fact,
that in these beds we find the first remains of the bodies of animated
creatures. My hypothesis may indeed be unsound; but, whether or not, it
is clear, taking organic remains as upon the whole a faithful chronicle,
that the deposition of these limestone beds was coeval with the existence
of the earliest, or all but the earliest, living creatures upon earth.
And what were those creatures? It might well be with a kind of awe that
the uninstructed inquirer would wait for an answer to this question. But
nature is simpler than man’s wit would make her, and behold, the
interrogation only brings before us the unpretending forms of various
zoophytes and polypes, together with a few single and double-valved
shell-fish (mollusks), all of them creatures of the sea. It is rather
surprising to find these before any vegetable forms, considering that
vegetables appear to us as forming the necessary first link in the chain
of nutrition; but it is probable that there were sea plants, and also
some simpler forms of animal life, before this period, although of too
slight a substance to leave any fossil trace of their existence.
The exact point in the ascending stratified series at which the first
traces of organic life are to be found is not clearly determined. Dr.
M’Culloch states that he found fossil orthocerata (a kind of shell-fish)
so early as the gneiss tract of Loch Eribol, in Sutherland; but Messrs.
Sedgwick and Murchison, on a subsequent search, could not verify the
discovery. It has also been stated, that the gneiss and mica tract of
Bohemia contains some seams of grawacke, in which are organic remains;
but British geologists have not as yet attached much importance to this
statement. We have to look a little higher in the series for indubitable
traces of organic life.
Above the gneiss and mica slate system, or group of strata, is the _Clay
Slate and Grawacke Slate System_; that is to say, it is higher in the
_order of supraposition_, though very often it rests immediately on the
primitive granite. The sub-groups of this system are in the following
succession upwards:—1, hornblende slate; 2, chiastolite slate; 3, clay
slate; 4, Snowdon rocks, (grawacke and conglomerates;) 5, Bala limestone;
6, Plynlymmon rocks, (grawacke and grawacke slates, with beds of
conglomerates.) This system is largely developed in the west and north
of England, and it has been well examined, partly because some of the
slate beds are extensively quarried for domestic purposes. If we
overlook the dubious statements respecting Sutherland and Bohemia, we
have in this “system” the first appearances of life upon our planet. The
animal remains are chiefly confined to the slate beds, those named from
Bala, in Wales, being the most prolific. _Zoophyta_, _polyparia_,
_crinoidea_, _conchifera_, and _crustacea_, {60} are the orders of the
animal kingdom thus found in the earliest of earth’s sepulchres. The
_orders_ are distinguished without difficulty, from the general
characters of the creatures whose remains are found; but it is only in
this general character that they bear a general resemblance to any
creatures now existing. When we come to consider specific characters, we
see that a difference exists—that, in short, the species and even genera
are no longer represented upon earth. More than this, it will be found
that the earliest species comparatively soon gave place to others, and
that they are not represented even in the next higher group of rocks.
One important remark has been made, that a comparatively small variety of
species is found in the older rocks, although of some particular ones the
remains are very abundant; as, for instance, of a species of asaphus,
which is found between the laminæ of some of the slate rocks of Wales,
and the corresponding rocks of Normandy and Germany in enormous
quantities.
Ascending to the next group of rocks, we find the traces of life become
more abundant, the number of species extended, and important additions
made in certain vestiges of fuci, or sea-plants, and of fishes. This
group of rocks has been called by English geologists, the _Silurian
System_, because largely developed at the surface of a district of
western England, formerly occupied by a people whom the Roman historians
call Silures. It is a series of sandstones, limestones, and beds of
shale (hardened mud), which are classed in the following sub-groups,
beginning with the undermost:—1, Llandillo rocks, (darkish calcareous
flagstones;) 2 and 3, two groups called Caradoc rocks; 4, Wenlock shale;
5, Wenlock limestone; 6, Lower Ludlow rocks, (shales and limestones;) 7,
Aymestry limestone; 8, Upper Ludlow rocks, (shales and limestone, chiefly
micaceous.) From the lowest beds upwards, there are polypiaria, though
most prevalent in the Wenlock limestone; conchifera, a vast number of
genera, but all of the order brachiopoda, (including terebratula,
pentamerus, spirifer, orthis, leptæna;) mollusca, of several orders and
many genera, (including turritella, orthoceras, nautilus, bellerophon;)
crustacea, all of them trilobites, (including trinucleus, asaphus,
calamene.) A little above the Llandillo rocks, there have been
discovered certain convoluted forms, which are now established as
annelids, or sea-worms, a tribe of creatures still existing, (nereidina
and serpulina,) and which may often be found beneath stones on a
sea-beach. One of these, figured by Mr. Murchison, is furnished with
feet in vast numbers all along its body, like a centipede. The
occurrence of annelids is important, on account of their character and
status in the animal kingdom. They are red-blooded and hermaphrodite,
and form a link of connexion between the annulosa (white-blooded worms)
and a humble class of the vertebrata. {62} The Wenlock limestone is most
remarkable amongst all the rocks of the Silurian system, for organic
remains. Many slabs of it are wholly composed of corals, shells, and
trilobites, held together by shale. It contains many genera of crinoidea
and polypiaria, and it is thought that some beds of it are wholly the
production of the latter creatures, or are, in other words, coral reefs
transformed by heat and pressure into rocks. Remains of fishes, of a
very minute size, have been detected by Mr. Philips in the Aymestry
limestone, being apparently the first examples of vertebrated animals
which breathed upon our planet. In the upper Ludlow rocks, remains of
six genera of fish have been for a longer period known; they belong to
the order of cartilaginous fishes, an order of mean organization and
ferocious habits, of which the shark and sturgeon are living specimens.
“Some were furnished with long palates, and squat, firmly-based teeth,
well adapted for crushing the strong-cased zoophytes and shells of the
period, fragments of which occur in the fœcal remains; some with teeth
that, like the fossil sharks of the later formations, resemble lines of
miniature pyramids, larger and smaller alternating; some with teeth
sharp, thin, and so deeply serrated, that every individual tooth
resembles a row of poniards set up against the walls of an armory; and
these last, says Agassiz, furnished with weapons so murderous, must have
been the pirates of the period. Some had their fins guarded with long
spines, hooked like the beak of an eagle; some with spines of straighter
and more slender form, and ribbed and furrowed longitudinally like
columns; some were shielded by an armour of bony points, and some thickly
covered with glistening scales.” {64}
The traces of fuci in this system are all but sufficient to allow of a
distinction of genera. In some parts of North America, extensive though
thin beds of them have been found. A distinguished French geologist, M.
Brogniart, has shewn that all existing marine plants are classifiable
with regard to the zones of climate; some being fitted for the torrid
zone, some for the temperate, some for the frigid. And he establishes
that the fuci of these early rocks speak of a torrid climate, although
they may be found in what are now temperate regions; he also states that
those of the higher rocks betoken, as we ascend, a gradually diminishing
temperature.
We thus early begin to find proofs of the general uniformity of organic
life over the surface of the earth, at the time when each particular
system of rocks was formed. Species identical with the remains in the
Wenlock limestone occur in the corresponding class of rocks in the Eifel,
and partially in the Harz, Norway, Russia, and Brittany. The situations
of the remains in Russia are fifteen hundred miles from the Wenlock beds;
but at the distance of between six and seven thousand from those,—namely,
in the vale of Mississippi, the same species are discovered. Uniformity
in animal life over large geographical areas argues uniformity in the
conditions of animal life; and hence arise some curious inferences.
Species, in the same low class of animals, are now much more limited; for
instance, the Red Sea gives different polypiaria, zoophytes, and
shell-fish, from the Mediterranean. It is the opinion of M. Brogniart,
that the uniformity which existed in the primeval times can only be
attributed to the temperature arising from the internal heat, which had
yet, as he supposes, been sufficiently great to overpower the ordinary
meteorological influences, and spread a tropical clime all over the
globe.
ERA OF THE OLD RED SANDSTONE—
FISHES ABUNDANT.
WE advance to a new chapter in this marvellous history—the era of the
_Old Red Sandstone System_. This term has been recently applied to a
series of strata, of enormous thickness in the whole mass, largely
developed in Herefordshire, Shropshire, Worcestershire, and South Wales;
also in the counties of Fife, Forfar, Moray, Cromarty, and Caithness; and
in Russia and North America, if not in many other parts of the world.
The particular strata forming the system are somewhat different in
different countries; but there is a general character to the extent of
these being a mixture of flagstones, marly rocks, and sandstones, usually
of a laminous structure, with conglomerates. There is also a schist
shewing the presence of bitumen; a remarkable new ingredient, since it is
a vegetable production. In the conglomerates, of great extent and
thickness, which form, in at least one district, the basis or leading
feature of the system, inclosing water-worn fragments of quartz and other
rocks, we have evidence of the seas of that period having been subjected
to a violent and long-continued agitation, probably from volcanic causes.
The upper members of the series bear the appearance of having been
deposited in comparatively tranquil seas. The English specimens of this
system shew a remarkable freedom from those disturbances which result in
the interjection of trap; and they are thus defective in mineral ores.
In some parts of England the old red sandstone system has been stated as
10,000 feet in thickness.
In this era, the forms of life which existed in the Silurian are
continued: we have the same orders of marine creatures, zoophyta,
polypiaria, conchifera, crustacea; but to these are added numerous
fishes, some of which are of most extraordinary and surprising forms.
Several of the strata are crowded with remains of fish, shewing that the
seas in which those beds were deposited had swarmed with that class of
inhabitants. The investigation of this system is recent; but already
{68} M. Agassiz has ascertained about twenty genera, and thrice the
number of species. And it is remarkable that the Silurian fishes are
here only represented in genera; the whole of the _species_ of that era
had already passed away. Even throughout the sub-groups of the system
itself, the species are changed; and these are phenomena observed
throughout all the subsequent systems or geological eras; apparently
arguing that, during the deposition of all the rocks, a gradual change of
physical conditions was constantly going on. A varying temperature, or
even a varying depth of sea, would at present be attended with similar
changes in marine life; and by analogy we are entitled to assume that
such variations in the ancient seas might be amongst the causes of that
constant change of genera and species in the inhabitants of those seas to
which the organic contents of the rocks bear witness.
Some of the fossils of this system,—the cephalaspis, coccosteus,
pterichthys, holoptychius—are, in form and structure, entirely different
from any fishes now existing, only the sturgeon family having any trace
of affinity to them in any respect. They seem to form a sort of
connecting link between the crustacea and true fishes.
The _cephalaspis_ may be considered as making the smallest advance from
the crustacean character; it very much resembles in form the asaphus of
lower formations, having a longish tail-like body inserted within the
cusp of a large crescent-shaped head, somewhat like a saddler’s
cutting-knife. The body is covered with strong plates of bone,
enamelled, and the head was protected on the upper side with one large
plate, as with a buckler—hence the name, implying _buckler-head_. A
range of small fins conveys the idea of its having been as weak in motion
as it is strong in structure. The _coccosteus_ may be said to mark the
next advance to fish creation. The outline of its body is of the form of
a short thick coffin, rounded, covered with strong bony plates, and
terminating in a long tail, which seems to have been the sole organ of
motion. It is very remarkable, that, while the tail establishes this
creature among the vertebrata and the fishes, its mouth has been opened
vertically, like those of the crustaceans, but which is contrary to the
mode of vertebrata generally. This seems a pretty strong mark of the
link character of the coccosteus between these two great departments of
the animal kingdom. The _pterichthys_ has also strong bony plates over
its body, arranged much like those of a tortoise, and has a long tail;
but its most remarkable feature, and that which has suggested its name,
is a pair of long and narrow wing-like appendages attached to the
shoulders, which the creature is supposed to have erected for its defence
when attacked by an enemy.
The _holoptychius_ is of a flat oval form, furnished with fins, and
ending in a long tail; the whole body covered with strong plates which
overlap each other, and the head forming only a slight rounded projection
from the general figure. The specimens in the lower beds are not above
the size of a flounder; but in the higher strata, to judge by the size of
the scales or plates which have been found, the creature attained a
comparatively monstrous size.
The other fishes of the system,—the osteolepis, glyptolepis, dipterus,
&c., are, in general outline, much like fishes still existing, but their
organization has, nevertheless, some striking peculiarities. They have
been entirely covered with bony scales or plates, enamelled externally;
their spines are tipped with bone, and, as one striking and unvarying
feature, the tail is only finned on the lower side. The internal
skeleton, of which no traces have been preserved, is presumed to have
been cartilaginous. They therefore unite the character of cartilaginous
fishes with a character peculiar to themselves, and in which we see
pretty clear vestiges of the pre-existent crustaceous form.
With regard to the link character of these animals, some curious facts
are mentioned. It appears that in the imperfect condition of the
vertebral column, and the inferior situation of the mouth in the
pterichthys, coccosteus, &c., there is an analogy to the form of the
dorsal cord and position of the mouth in the embryo of perfect fishes.
The one-sided form of the tail in the osteolepis &c. finds a similar
analogy in the form of the tail in the embryo of the salmon. It is not
premature to remark how broadly these facts seem to hint at a parity of
law affecting the progress of general creation, and the progress of an
individual fœtus of one of the more perfect animals.
It is equally ascertained of the types of being prevalent in the old red,
as of those of the preceding system, that they are uniform in the
corresponding strata of distant parts of the earth; for instance, Russia
and North America.
In the old red sandstone, the marine plants, of which faint traces are
observable in the Silurians, continue to appear. It would seem as if
less change took place in the vegetation than in the animals of those
early seas; and for this, as Mr. Miller has remarked, it is easy to
imagine reasons. For example, an infusion of lime into the sea would
destroy animal life, but be favourable to vegetation.
As yet there were no land animals or plants, and for this the presumable
reason is, that no dry land as yet existed. We are not left to make this
inference solely from the absence of land animals and plants; in the
arrangement of the primary (stratified) rocks, we have further evidence
of it. That these rocks were formed in a generally horizontal position,
we are as well assured as that they were formed at the bottom of seas.
But they are always found greatly inclined in position, tilted up against
the slopes of the granitic masses which are beneath them in geological
order, though often shooting up to a higher point in the atmosphere. No
doubt can be entertained that these granitic masses, forming our
principal mountain ranges, have been protruded from below, or, at least,
thrust much further up, _since_ the deposition of the primary rocks. The
protrusion was what tilted up the primary rocks; and the inference is, of
course, unavoidable, that these mountains have risen chiefly, at least,
since the primary rocks were laid down. It is remarkable that, while the
primary rocks thus incline towards granitic nuclei or axes, the strata
higher in the series rest against these again, generally at a less
inclination, or none at all, shewing that these strata were laid down
after the swelling mountain eminences had, by their protrusion, tilted up
the primary strata. And thus it may be said an era of local upthrowing
of the primitive and (perhaps) central matter of our planet, is
established as happening about the close of the primary strata, and
beginning of the next ensuing system. It may be called the _Era of the
Oldest Mountains_, or, more boldly, of the formation of the detached
portions of dry land over the hitherto watery surface of the globe—an
important part of the designs of Providence, for which the time was now
apparently come. It may be remarked, that volcanic disturbances and
protrusions of trap took place throughout the whole period of the
deposition of the primary rocks; but they were upon a comparatively
limited scale, and probably all took place under water. It was only now
that the central granitic masses of the great mountain ranges were thrown
up, carrying up with them broken edges of the primary strata; a process
which seems to have had this difference from the other, that it was the
effect of a more tremendous force exerted at a lower depth in the earth,
and generally acting in lines pervading a considerable portion of the
earth’s surface. We shall by-and-by see that the protrusion of some of
the mountain ranges was not completed, or did not stop, at that period.
There is no part of geological science more clear than that which refers
to the ages of mountains. It is as certain that the Grampian mountains
of Scotland are older than the Alps and Apennines, as it is that
civilization had visited Italy, and had enabled her to subdue the world,
while Scotland was the residence of “roving barbarians.” The Pyrenees,
Carpathians, and other ranges of continental Europe, are all younger than
the Grampians, or even the insignificant Mendip Hills of southern
England. Stratification tells this tale as plainly as Livy tells the
history of the Roman republic. It tells us—to use the words of Professor
Philips—that at the time when the Grampians sent streams and detritus to
straits where now the valleys of the Forth and Clyde meet, the greater
part of Europe was a wide ocean.
The last three systems—called, in England, the Cumbrian, Silurian, and
Devonian, and collectively the palæozoic rocks, from their containing the
remains of the earliest inhabitants of the globe—are of vast thickness;
in England, not much less than 30,000 feet, or nearly six miles. In
other parts of the world, as we have seen, the earliest of these systems
alone is of much greater depth—arguing an enormous profundity in the
ocean in which they were formed.
SECONDARY ROCKS.
ERA OF THE CARBONIFEROUS FORMATION.
LAND FORMED.
COMMENCEMENT OF LAND PLANTS.
WE now enter upon a new great epoch in the history of our globe. There
was now dry land. As a consequence of this fact, there was fresh water,
for rain, instead of immediately returning to the sea, as formerly, was
now gathered in channels of the earth, and became springs, rivers, and
lakes. There was now a theatre for the existence of land plants and
animals, and it remains to be inquired if these accordingly were
produced.
The Secondary Rocks, in which our further researches are to be
prosecuted, consist of a great and varied series, resting, generally
unconformably, against flanks of the upturned primary rocks, sometimes
themselves considerably inclined, at others, forming extensive basin-like
beds, nearly horizontal; in many places, much broken up and shifted by
disturbances from below. They have all been formed out of the materials
of the older rocks, by virtue of the wearing power of air and water,
which is still every day carrying down vast quantities of the elevated
matter of the globe into the sea. But the separate strata are each much
more distinct in the matter of its composition than might be expected.
Some are siliceous or arenaceous (sandstones), composed mainly of fine
grains from the quartz rocks—the most abundant of the primary strata.
Others are argillaceous—clays, shales, &c., chiefly derived, probably,
from the slate beds of the primary series. Others are calcareous,
derived from the early limestone. As a general feature, they are softer
and less crystalline than the primary rocks, as if they had endured less
of both heat and pressure than the senior formation. There are beds
(_coal_) formed solely of vegetable matter, and some others in which the
main ingredient is particles of iron, (_the iron black band_.) The
secondary rocks are quite as communicative with regard to their portion
of the earth’s history as the primitive were.
The first, or lowest, group of the secondary rocks is called the
_Carboniferous Formation_, from the remarkable feature of its numerous
interspersed beds of coal. It commences with the beds of the _mountain
limestone_, which, in some situations, as in Derbyshire and Ireland, are
of great thickness, being alternated with chert (a siliceous sandstone),
sandstones, shales, and beds of coal, generally of the harder and less
bituminous kind (_anthracite_), the whole being covered in some places by
the millstone grit, a siliceous conglomerate composed of the detritus of
the primary rocks. The mountain limestone, attaining in England to a
depth of eight hundred yards, greatly exceeds in volume any of the
primary limestone beds, and shews an enormous addition of power to the
causes formerly suggested as having produced this substance. In fact,
remains of corals, crinoidea, and shells, are so abundant in it, as to
compose three-fourths of the mass in some parts. Above the mountain
limestone commence the more conspicuous _coal beds_, alternating with
sandstones, shales, beds of limestone, and ironstone. Coal is altogether
composed of the matter of a terrestrial vegetation, transmuted by
pressure. Some fresh-water shells have been found in it, but few of
marine origin, and no remains of those zoophytes and crinoidea so
abundant in the mountain limestone and other rocks. Coal beds exist in
Europe, Asia, and America, and have hitherto been esteemed as the most
valuable of mineral productions, from the important services which the
substance renders in manufactures and in domestic economy. It is to be
remarked, that there are some local variations in the arrangement of coal
beds. In France, they rest immediately on the granite and other primary
rocks, the intermediate strata not having been found at those places. In
America, the kind called anthracite occurs among the slate beds, and this
species also abounds more in the mountain limestone than with us. These
last circumstances only shew that different parts of the earth’s surface
did not all witness the same events of a certain fixed series exactly at
the same time. There had been an exhibition of dry land about the site
of America, a little earlier than in Europe.
Some features of the condition of the earth during the deposition of the
carboniferous group, are made out with a clearness which must satisfy
most minds. First we are told of a time when carbonate of lime was
formed in vast abundance at the bottoms of profound seas, accompanied by
an unusually large population of corals and encrinites; while in some
parts of the earth there were patches of dry land, covered with a
luxuriant vegetation. Next we have a comparatively brief period of
volcanic disturbance, (when the conglomerate was formed.) Then the
causes favourable to the so abundant production of limestone, and the
large population of marine acrita, decline, and we find the masses of dry
land increase in number and extent, and begin to bear an amount of forest
vegetation, far exceeding that of the most sheltered tropical spots of
the present surface. The climate, even in the latitude of Baffin’s Bay,
was torrid, and perhaps the atmosphere contained a larger charge of
carbonic acid gas (the material of vegetation) than it now does. The
forests or thickets of the period, included no species of plants now
known upon earth. They mainly consisted of gigantic shrubs, which are
either not represented by any existing types, or are akin to kinds which
are now only found in small and lowly forms. That these forests grew
upon a Polynesia, or multitude of small islands, is considered probable,
from similar vegetation being now found in such situations within the
tropics. With regard to the circumstances under which the masses of
vegetable matter were transformed into successive coal strata, geologists
are divided. From examples seen at the present day, at the mouths of
such rivers as the Mississippi, which traverse extensive sylvan regions,
and from other circumstances to be adverted to, it is held likely by some
that the vegetable matter, the rubbish of decayed forests, was carried by
rivers into estuaries, and there accumulated in vast natural rafts, until
it sunk to the bottom, where an overlayer of sand or mud would prepare it
for becoming a stratum of coal. Others conceive that the vegetation
first went into the condition of a peat moss, that a sink in the level
then exposed it to be overrun by the sea, and covered with a layer of
sand or mud; that a subsequent uprise made the mud dry land, and fitted
it to bear a new forest, which afterwards, like its predecessor, became a
bed of peat; that, in short, by repetitions of this process, the
alternate layers of coal, sandstone, and shale, constituting the
carboniferous group, were formed. It is favourable to this last view
that marine fossils are scarcely found in the body of the coal itself,
though abundant in the shale layers above and below it; also that in
several places erect stems of trees are found with their roots still
fixed in the shale beds, and crossing the sandstone beds at almost right
angles, shewing that these, at least, had not been drifted from their
original situations. On the other hand, it is not easy to admit such
repeated risings and sinkings of surface as would be required, on this
hypothesis, to form a series of coal strata. Perhaps we may most safely
rest at present with the supposition that coal has been formed under both
classes of circumstances, though in the latter only as an exception to
the former.
Upwards of three hundred species of plants have been ascertained to exist
in the coal formation; but it is not necessary to suppose that the whole
contained in that system are now, or ever will be distinguished.
Experiments shew that some great classes of plants become decomposed in
water in a much less space of time than others, and it is remarkable that
those which decompose soonest, are of the classes found most rare, or not
at all, in the coal strata. It is consequently to be inferred that there
may have been grasses and mosses at this era, and many species of trees,
the remains of which had lost all trace of organic form before their
substance sunk into the mass of which coal was formed. In speaking,
therefore, of the vegetation of this period, we must bear in mind that it
may have comprehended forms of which we have no memorial.
Supposing, nevertheless, that, in the main, the ascertained vegetation of
the coal system is that which grew at the time of its formation, it is
interesting to find that the terrestrial botany of our globe begins with
classes of comparatively simple forms and structure. In the ranks of the
vegetable kingdom, the lowest place is taken by plants of cellular
tissue, and which have no flowers, (_cryptogamia_,) as lichens, mosses,
fungi, ferns, sea-weeds. Above these stand plants of vascular tissue,
and bearing flowers, in which again there are two great subdivisions;
first, plants having one seed-lobe, (_monocotyledons_,) and in which the
new matter is added within, (_endogenous_,) of which the cane and palm
are examples; second, plants having two seed-lobes, (_dicotyledons_,) and
in which the new matter is added on the outside under the bark,
(_exogenous_,) of which the pine, elm, oak, and most of the British
forest-trees are examples; these subdivisions also ranking in the order
in which they are here stated. Now it is clear that a predominance of
these forms in succession marked the successive epochs developed by
fossil geology; the simple abounding first, and the complex afterwards.
Two-thirds of the plants of the carboniferous era are of the cellular or
cryptogamic kind, a proportion which would probably be much increased if
we knew the whole Flora of that era. The ascertained dicotyledons, or
higher-class plants, are comparatively few in this formation; but it will
be found that they constantly increased as the globe grew older.
The master-form or type of the era was the _fern_, or breckan, of which
about one hundred and thirty species have already been ascertained as
entering into the composition of coal. {84a} The fern is a plant which
thrives best in warm, shaded, and moist situations. In tropical
countries, where these conditions abound, there are many more species
than in temperate climes, and some of these are arborescent, or of a
tree-like size and luxuriance. {84b} The ferns of the coal strata have
been of this magnitude, and that without regard to the parts of the earth
where they are found. In the coal of Baffin’s Bay, of Newcastle, and of
the torrid zone alike, are the fossil ferns arborescent, shewing clearly
that, in that era, the present tropical temperature, or one even higher,
existed in very high latitudes.
In the swamps and ditches of England there grows a plant called the
horse-tail (_equisetum_), having a succulent, erect, jointed stem, with
slender leaves, and a scaly catkin at the top. A second large section of
the plants of the carboniferous era were of this kind (_equisetaceæ_),
but, like the fern, reaching the magnitudes of trees. While existing
equiseta rarely exceed three feet in height, and the stems are generally
under half an inch in diameter, their kindred, entombed in the coal beds,
seem to have been generally fourteen or fifteen feet high, with stems
from six inches to a foot in thickness. Arborescent plants of this
family, like the arborescent ferns, now grow only in tropical countries,
and their being found in the coal beds in all latitudes is consequently
held as an additional proof, that at this era a warm climate was extended
much farther to the north than at present. It is to be remarked that
plants of this kind (forming two genera, the most abundant of which is
the _calamites_) are only represented on the present surface by plants of
the same _family_: the _species_ which flourished at this era gradually
lessen in number as we advance upwards in the series of rocks, and
disappear before we arrive at the tertiary formation.
The club-moss family (_lycopodiaceæ_) are other plants of the present
surface, usually seen in a lowly and creeping form in temperate
latitudes, but presenting species which rise to a greater magnitude
within the tropics. Many specimens of this family are found in the coal
beds; it is thought they have contributed more to the substance of the
coal than any other family. But, like the ferns and equisetaceæ, they
rise to a prodigious magnitude. The lepidodendra (so the fossil genus is
called) have probably been from sixty-five to eighty feet in height,
having at their base a diameter of about three feet, while their leaves
measured twenty inches in length. In the forests of the coal era, the
lepidodendra would enjoy the rank of firs in our forests, affording shade
to the only less stately ferns and calamites. The internal structure of
the stem, and the character of the seed-vessels, shew them to have been a
link between single-lobed and double-lobed plants, a fact worthy of note,
as it favours the idea that, in vegetable, as well as animal creation, a
progress has been observed, in conformity with advancing conditions. It
is also curious to find a missing link of so much importance in a genus
of plants which has long ceased to have a living place upon earth.
The other leading plants of the coal era are without representatives on
the present surface, and their characters are in general less clearly
ascertained. Amongst the most remarkable are—the _sigillaria_, of which
large stems are very abundant, shewing that the interior has been soft,
and the exterior fluted with separate leaves inserted in vertical rows
along the flutings—and the _stigmaria_, plants apparently calculated to
flourish in marshes or pools, having a short, thick, fleshy stem, with a
dome-shaped top, from which sprung branches of from twenty to thirty feet
long. Amongst monocotyledons were some palms, (_flabellaria_ and
_næggerathia_,) besides a few not distinctly assignable to any class.
The dicotyledons of the coal are comparatively few, though on the present
surface they are the most numerous sub-class. Besides some of doubtful
affinity, (_annularia_, _asterophyllites_, &c.,) there were a few of the
pine family, which seem to have been the highest class of trees of this
era, and are only as yet found in isolated cases, and in sandstone beds.
The first discovered lay in the Craigleith quarry, near Edinburgh, and
consisted of a stem about two feet thick, and forty-seven feet in length.
Others have since been found, both in the same situation, and at
Newcastle. Leaves and fruit being wanting, an ingenious mode of
detecting the nature of these trees was hit upon by Mr. Witham of
Lartington. Taking thin polished cross slices of the stem, and
subjecting them to the microscope, he detected the structure of the wood
to be that of a cone-bearing tree, by the presence of certain
“reticulations” which distinguish that family, in addition to the usual
radiating and concentric lines. That particular tree was concluded to be
an araucaria, a species now found in Norfolk Island, in the South Sea,
and in a few other remote situations. The coniferæ of this era form the
dawn of dicotyledenous trees, of which they may be said to be the
simplest type, and to which, it has already been noticed, the
lepidodendra are a link from the monocotyledons. The concentric rings of
the Craigleith and other coniferæ of this era have been mentioned. It is
interesting to find in these a record of the changing seasons of those
early ages, when as yet there were no human beings to observe time or
tide. They are clearly traced; but it is observed that they are more
slightly marked than is the case with their family at the present day, as
if the changes of temperature had been within a narrower range.
Such was the vegetation of the carbonigenous era, composed of forms at
the bottom of the botanical scale, flowerless, fruitless, but luxuriant
and abundant beyond what the most favoured spots on earth can now shew.
The rigidity of the leaves of its plants, and the absence of fleshy
fruits and farinaceous seeds, unfitted it to afford nutriment to animals;
and, monotonous in its forms, and destitute of brilliant colouring, its
sward probably unenlivened by any of the smaller flowering herbs, its
shades uncheered by the hum of insects, or the music of birds, it must
have been but a sombre scene to a human visitant. But neither man nor
any other animals were then in existence to look for such uses or such
beauties in this vegetation. It was serving other and equally important
ends, clearing (probably) the atmosphere of matter noxious to animal
life, and storing up mineral masses which were in long subsequent ages to
prove of the greatest service to the human race, even to the extent of
favouring the progress of its civilization.
The animal remains of this era are not numerous, in comparison with those
which go before, or those which come after. The mountain limestone,
indeed, deposited at the commencement of it, abounds unusually in
polypiaria and crinoidea; but when we ascend to the coal-beds themselves,
the case is altered, and these marine remains altogether disappear. We
have then only a limited variety of conchifers and shell mollusks, with
fragments of a few species of fishes, and these are rarely or never found
in the coal seams, but in the shales alternating with them. Some of the
fishes are of a sauroid character, that is, partake of the nature of the
lizard, a genus of the reptilia, a land class of animals, so that we may
be said here to have the first approach to a kind of animals calculated
to breathe the atmosphere. Such is the Megalichthys Hibbertii, found by
Dr. Hibbert Ware, in a limestone bed of fresh-water origin, underneath
the coal at Burdiehouse, near Edinburgh. Others of the same kind have
been found in the coal measures in Yorkshire, and in the low coal shales
at Manchester. This is no more than might be expected, as collections of
fresh water now existed, and it is presumable that they would be peopled.
The chief other fishes of the coal era are named palæothrissum,
palæoniscus, diperdus.
Coal strata are nearly confined to the group termed the carboniferous
formation. Thin beds are not unknown afterwards, but they occur only as
a rare exception. It is therefore thought that the most important of the
conditions which allowed of so abundant a terrestrial vegetation, had
ceased about the time when this formation was closed. The high
temperature was not one of the conditions which terminated, for there are
evidences of it afterwards; but probably the superabundance of carbonic
acid gas supposed to have existed during this era was expended before its
close. There can be little doubt that the infusion of a large dose of
this gas into the atmosphere at the present day would be attended by
precisely the same circumstances as in the time of the carboniferous
formation. Land animal life would not have a place on earth; vegetation
would be enormous; and coal strata would be formed from the vast
accumulations of woody matter, which would gather in every sea, near the
mouths of great rivers. On the exhaustion of the superabundance of
carbonic acid gas, the coal formation would cease, and the earth might
again become a suitable theatre of being for land animals.
The termination of the carboniferous formation is marked by symptoms of
volcanic violence, which some geologists have considered to denote the
close of one system of things and the beginning of another. Coal beds
generally lie in basins, as if following the curve of the bottom of seas.
But there is no such basin which is not broken up into pieces, some of
which have been tossed up on edge, others allowed to sink, causing the
ends of strata to be in some instances many yards, and in a few several
hundred feet, removed from the corresponding ends of neighbouring
fragments. These are held to be results of volcanic movements below, the
operation of which is further seen in numerous upbursts and intrusions of
volcanic rock (trap). That these disturbances took place about the close
of the formation, and not later, is shewn in the fact of the next higher
group of strata being comparatively undisturbed. Other symptoms of this
time of violence are seen in the beds of conglomerate which occur amongst
the first strata above the coal. These, as usual, consist of fragments
of the elder rocks, more or less worn from being tumbled about in
agitated water, and laid down in a mud paste, afterwards hardened.
Volcanic disturbances break up the rocks; the pieces are worn in seas;
and a deposit of conglomerate is the consequence. Of porphyry, there are
some such pieces in the conglomerate of Devonshire, three or four tons in
weight. It is to be admitted for strict truth that, in some parts of
Europe, the carboniferous formation is followed by superior deposits,
without the appearance of such disturbances between their respective
periods; but apparently this case belongs to the class of exceptions
already noticed. {93} That disturbance was general, is supported by the
further and important fact of the destruction of many forms of organic
being previously flourishing, particularly of the vegetable kingdom.
ERA OF THE NEW RED SANDSTONE.
TERRESTRIAL ZOOLOGY COMMENCES
WITH REPTILES.
FIRST TRACES OF BIRDS.
THE next volume of the rock series refers to an era distinguished by an
event of no less importance than the commencement of land animals. The
_New Red Sandstone System_ is subdivided into groups, some of which are
wanting in some places; they are pretty fully developed in the north of
England, in the following ascending order:—1. Lower red sandstone; 2.
Magnesian limestone; 3. Red and white sandstones and conglomerate; 4.
Variegated marls. Between the third and fourth there is, in Germany,
another group, called the Muschelkalk, a word expressing a limestone full
of shells.
The first group, containing the conglomerates already adverted to, seems
to have been produced during the time of disturbance which occurred so
generally after the carbonigenous era. This new era is distinguished by
a paucity of organic remains, as might partly be expected from the
appearances of disturbance, and the red tint of the rocks, the latter
being communicated by a solution of oxide of iron, a substance
unfavourable to animal life.
The second group is a limestone with an infusion of magnesia. It is
developed less generally than some others, but occurs conspicuously in
England and Germany. Its place, above the red sandstone, shews the
recurrence of circumstances favourable to animal life, and we accordingly
find in it not only zoophytes, conchifera, and a few tribes of fish, but
some faint traces of land plants, and a new and startling appearance—a
reptile of saurian (lizard) character, analogous to the now existing
family called monitors. Remains of this creature are found in
cupriferous (copper-bearing) slate connected with the mountain limestone,
at Mansfield and Glucksbrunn, in Germany, which may be taken as evidence
that dry land existed in that age near those places. The magnesia
limestone is also remarkable as the last rock in which appears the
leptæna, or producta, a conchifer of numerous species which makes a
conspicuous appearance in all previous seas. It is likewise to be
observed, that the fishes of this age, to the genera of which the names
palæoniscus, catopterus, platysomus, &c., have been applied, vanish, and
henceforth appear no more.
The third group, chiefly sandstones, variously coloured according to the
amount and nature of the metallic oxide infused into them, shews a
recurrence of agitation, and a consequent diminution of the amount of
animal life. In the upper part, however, of this group, there are
abundant symptoms of a revival of proper conditions for such life. There
are marl beds, the origin of which substance in decomposed shells is
obvious; and in Germany, though not in England, here occurs the
muschelkalk, containing numerous organic remains, (generally different
from those of the magnesian limestone,) and noted for the specimens of
land animals, which it is the first to present in any considerable
abundance to our notice.
These animals are of the vertebrate sub-kingdom, but of its lowest class
next after fishes,—namely, reptiles,—a portion of the terrestrial tribes
whose imperfect respiratory system perhaps fitted them for enduring an
atmosphere not yet quite suitable for birds or mammifers. {97} The
specimens found in the muschelkalk are allied to the crocodile and lizard
tribes of the present day, but in the latter instance are upon a scale of
magnitude as much superior to present forms as the lepidodendron of the
coal era was superior to the dwarf club-mosses of our time. These
saurians also combine some peculiarities of structure of a most
extraordinary character.
The animal to which the name _ichthyosaurus_ has been given, was as long
as a young whale, and it was fitted for living in the water, though
breathing the atmosphere. It had the vertebral column and general bodily
form of a fish, but to that were added the head and breast-bone of a
lizard, and the paddles of the whale tribes. The beak, moreover, was
that of a porpoise, and the teeth were those of a crocodile. It must
have been a most destructive creature to the fish of those early seas.
The _plesiosaurus_ was of similar bulk, with a turtle-like body and
paddles, shewing that the sea was its element, but with a long
serpent-like neck, terminating in a saurian head, calculated to reach
prey at a considerable distance. These two animals, of which many
varieties have been discovered, constituting distinct species, are
supposed to have lived in the shallow borders of the seas of this and
subsequent formations, devouring immense quantities of the finny tribes.
It was at first thought that no creatures approaching them in character
now inhabit the earth; but latterly Mr. Darwin has discovered, in the
reptile-peopled Galapagos Islands, in the South Sea, a marine saurian
from three to four feet long.
The _megalosaurus_ was an enormous lizard—a land creature, also
carnivorous. The _pterodactyle_ was another lizard, but furnished with
wings to pursue its prey in the air, and varying in size between a
cormorant and a snipe. Crocodiles abounded, and some of these were
herbivorous. Such was the iguanodon, a creature of the character of the
iguana of the Ganges, but reaching a hundred feet in length, or twenty
times that of its modern representative.
There were also numerous _tortoises_, some of them reaching a great size;
and Professor Owen has found in Warwickshire some remains of an animal of
the batrachian order, {99} to which, from the peculiar form of the teeth,
he has given the name of labyrinthidon. Thus, three of Cuvier’s four
orders of reptilia (_sauria_, _chelonia_, and _batrachia_) are
represented in this formation, the serpent order (_ophidia_) being alone
wanting.
The variegated marl beds which constitute the uppermost group of the
formation, present two additional genera of huge saurians,—the
phytosaurus and mastodonsaurus.
It is in the upper beds of the red sandstone that beds of salt first
occur. These are sometimes of such thickness, that the mine from which
the material has been excavated looks like a lofty church. We see in the
present world no circumstances calculated to produce the formation of a
bed of rock salt; yet it is not difficult to understand how such strata
were formed in an age marked by ultra-tropical heat and frequent volcanic
disturbances. An estuary, cut off by an upthrow of trap, or a change of
level, and left to dry up under the heat of the sun, would quickly become
the bed of a dense layer of rock salt. A second shift of level, or some
other volcanic disturbance, connecting it again with the sea, would
expose this stratum to being covered over with a layer of sand or mud,
destined in time to form the next stratum of rock above it.
The plants of this era are few and unobtrusive. Equiseta, calamites,
ferns, Voltzia, and a few of the other families found so abundantly in
the preceding formation, here present themselves, but in diminished size
and quantity.
This seems to be the proper place to advert to certain memorials of a
peculiar and unexpected character respecting these early ages in the
sandstones. So low as the bottom of the carboniferous system, slabs are
found marked over a great extent of surface with that peculiar
corrugation or wrinkling which the receding tide leaves upon a sandy
beach when the sea is but slightly agitated; and not only are these
ripple-marks, as they are called, found on the surfaces, but casts of
them are found on the under sides of slabs lying above. The phenomena
suggests the time when the sand ultimately formed into these stone slabs,
was part of the beach of a sea of the carbonigenous era; when, left wavy
by one tide, it was covered over with a thin layer of fresh sand by the
next, and so on, precisely as such circumstances might be expected to
take place at the present day. Sandstone surfaces, ripple-marked, are
found throughout the subsequent formations: in those of the new red, at
more than one place in England, they further bear impressions of
rain-drops which have fallen upon them—the rain, of course, of the
inconceivably remote age in which the sandstones were formed. In the
Greensill sandstone, near Shrewsbury, it has even been possible to tell
from what direction the shower came which impressed the sandy surface,
the rims of the marks being somewhat raised on one side, exactly as might
be expected from a slanting shower falling at this day upon one of our
beaches. These facts have the same sort of interest as the season rings
of the Craigleith conifers, as speaking of a parity between some of the
familiar processes of nature in those early ages and our own.
In the new red sandstone, impressions still more important in the
inferences to which they tend, have been observed,—namely, the footmarks
of various animals. In a quarry of this formation, at Corncockle Muir,
in Dumfriesshire, where the slabs incline at an angle of thirty-eight
degrees, the vestiges of an animal supposed to have been a tortoise are
distinctly traced up and down the slope, as if the creature had had
occasion to pass backwards and forwards in that direction only, possibly
in its daily visits to the sea. Some slabs similarly impressed, in the
Stourton quarries in Cheshire, are further marked with a shower of rain
which we know must have fallen _afterwards_, for its little hollows are
impressed in the footmarks also, though more slightly than on the rest of
the surface, the comparative hardness of a trodden place having
apparently prevented so deep an impression being made. At Hessberg, in
Saxony, the vestiges of four distinct animals have been traced, one of
them a web-footed animal of small size, considered as a congener of the
crocodile; another, whose footsteps having a resemblance to an impression
of a swelled human hand, has caused it to be named the _cheirotherium_.
The footsteps of the cheirotherium have been found also in the Stourton
quarries above mentioned. Professor Owen, who stands at the head of
comparative anatomy in the present day, has expressed his belief that
this last animal was the same batrachian of which he has found fragments
in the new red sandstone of Warwickshire. At Runcorn, near Manchester,
and elsewhere, have been discovered the tracks of an animal which Mr.
Owen calls the rynchosaurus, uniting with the body of a reptile the beak
and feet of a bird, and which clearly had been a _link_ between these two
classes.
If geologists shall ultimately give their approbation to the inferences
made from a recent discovery in America, we shall have the addition of
perfect birds, though probably of a low type, to the animal forms of this
era. It is stated to be in quarries of this rock, in the valley of
Connecticut, that footprints have been found, apparently produced by
birds of the order grallæ, or waders. “The footsteps appear in regular
succession on the continuous track of an animal, in the act of walking or
running, with the right and left foot always in their relative places.
The distance of the intervals between each footstep on the same track is
occasionally varied, but to no greater amount than may be explained by
the bird having altered its pace. Many tracks of different individuals
and different species are often found crossing each other, and crowded,
like impressions of feet upon the shores of a muddy stream, where ducks
and geese resort.” {103} Some of these prints indicate small animals,
but others denote birds of what would now be an unusually large size.
One animal, having a foot fifteen inches in length, (one-half more than
that of the ostrich,) and a stride of from four to six feet, has been
appropriately entitled, _ornithichnites giganteus_.
ERA OF THE OOLITE.
COMMENCEMENT OF MAMMALIA.
THE chronicles of this period consist of a series of beds, mostly
calcareous, taking their general name (_Oolite System_) from a
conspicuous member of them—the oolite—a limestone composed of an
aggregation of small round grains or spherules, and so called from its
fancied resemblance to a cluster of eggs, or the roe of a fish. This
texture of stone is novel and striking. It is supposed to be of chemical
origin, each spherule being an aggregation of particles round a central
nucleus. The oolite system is largely developed in England, France,
Westphalia, and Northern Italy; it appears in Northern India and Africa,
and patches of it exist in Scotland, and in the vale of the Mississippi.
It may of course be yet discovered in many other parts of the world.
The series, as shewn in the neighbourhood of Bath, is (beginning with the
lowest) as follows:—1. Lias, a set of strata variously composed of
limestone, clay, marl, and shale, clay being predominant; 2. Lower
oolitic formation, including, besides the great oolite bed of central
England, fullers’ earth beds, forest marble, and cornbrash; 3. Middle
oolitic formation, composed of two sub-groups, the Oxford clay and coral
rag, the latter being a mere layer of the works of the coral polype; 4.
Upper oolitic formation, including what are called Kimmeridge clay and
Portland oolite. In Yorkshire there is an additional group above the
lias, and in Sutherlandshire there is another group above that again. In
the wealds (moorlands) of Kent and Sussex, there is, in like manner,
above the fourth of the Bath series, another additional group, to which
the name of the _Wealden_ has been given, from its situation, and which,
composed of sandstones and clays, is subdivided into Purbeck beds,
Hastings sand, and Weald clay.
There are no particular appearances of disturbance between the close of
the new red sandstone and the beginning of the oolite system, as far as
has been observed in England. Yet there is a great change in the
materials of the rocks of the two formations, shewing that while the
bottoms of the seas of the one period had been chiefly arenaceous, those
of the other were chiefly clayey and limy. And there is an equal
difference between the two periods in respect of both botany and zoology.
While the new red sandstone shews comparatively scanty traces of organic
creation, those in the oolite are extremely abundant, particularly in the
department of animals, and more particularly still of sea mollusca,
which, it has been observed, are always the more conspicuous in
proportion to the predominance of calcareous rocks. It is also
remarkable that the animals of the oolitic system are entirely different
in species from those of the preceding age, and that these species cease
before the next. In this system we likewise find that uniformity over
great space which has been remarked of the Faunas of earlier formations.
“In the equivalent deposits in the Himalaya Mountains, at Fernando Po, in
the region north of the Cape of Good Hope, and in the Run of Cutch, and
other parts of Hindostan, fossils have been discovered, which, as far as
English naturalists who have seen them can determine, are
undistinguishable from certain oolite and lias fossils of Europe.” {108a}
The dry land of this age presented cycadeæ, “a beautiful class of plants
between the palms and conifers, having a tall, straight trunk,
terminating in a magnificent crown of foliage.” {108b} There were tree
ferns, but in smaller proportion than in former ages; also equisetaceæ,
lilia, and conifers. The vegetation was generally analogous to that of
the Cape of Good Hope and Australia, which seems to argue a climate (we
must remember, a universal climate) between the tropical and temperate.
It was, however, sufficiently luxuriant in some instances to produce thin
seams of coal, for such are found in the oolite formation of both
Yorkshire and Sutherland. The sea, as for ages before, contained algæ,
of which, however, only a few species have been preserved to our day.
The lower classes of the inhabitants of the ocean were unprecedentedly
abundant. The polypiaria were in such abundance as to form whole strata
of themselves. The crinoidea and echinites were also extremely numerous.
Shell mollusks, in hundreds of new species, occupied the bottoms of the
seas of those ages, while of the swimming shell-fish, ammonites and
belemnites, there were also many scores of varieties. The belemnite here
calls for some particular notice. It commences in the oolite, and
terminates in the next formation. It is an elongated, conical shell,
terminating in a point, and having, at the larger end, a cavity for the
residence of the animal, with a series of air-chambers below. The
animal, placed in the upper cavity, could raise or depress itself in the
water at pleasure by a pneumatic operation upon the entral air tube
pervading its shell. Its tentacula, sent abroad over the summit of the
shell, searched the sea for prey. The creature had an ink-bag, with
which it could muddle the water around it, to protect itself from more
powerful animals, and, strange to say, this has been found so well
preserved that an artist has used it in one instance as a paint,
wherewith to delineate the belemnite itself.
The crustacea discovered in this formation are less numerous. There are
many fishes, some of which (_acrodus_, _psammodus_, &c.,) are presumed
from remains of their palatal bones, to have been of the gigantic
cartilaginous class, now represented by such as the cestraceon. It has
been considered by Professor Owen as worthy of notice, that, the
cestraceon being an inhabitant of the Australian seas, we have, in both
the botany and ichthyology of this period, an analogy to that continent.
The pycnodontes, (thick-toothed,) and lepidoides, (having thick scales,)
are other families described by M. Agassiz as extensively prevalent. In
the shallow waters of the oolitic formation, the ichthyosaurus,
plesiosaurus, and other huge saurian carnivora of the preceding age,
plied, in increased numbers, their destructive vocation. {110} To them
were added new genera, the cetiosaurus, mososaurus, and some others, all
of similar character and habits.
Land reptiles abounded, including species of the pterodactyle of the
preceding age—tortoises, trionyces, crocodilians—and the pliosaurus, a
creature which appears to have formed a link between the plesiosaurus and
the crocodile. We know of at least six species of the flying saurian,
the pterodactyle, in this formation.
Now, for the first time, we find remains of insects, an order of animals
not well calculated for fossil preservation, and which are therefore
amongst the rarest of the animal tribes found in rocks, though they are
the most numerous of all living families. A single libellula
(dragon-fly) was found in the Stonesfield slate, a member of the lower
oolitic group quarried near Oxford; and this was for several years the
only specimen known to exist so early; but now many species have been
found in a corresponding rock at Solenhofen, in Germany. It is
remarkable that the remains of insects are found most plentifully near
the remains of pterodactyles, to which undoubtedly they served as prey.
The first glimpse of the highest class of the vertebrate
sub-kingdom—_mammalia_—is obtained from the Stonesfield slate, where
there has been found the jaw-bone of a quadruped evidently insectivorous,
and inferred, from peculiarities in the structure of that small fragment,
to have belonged to the marsupial family, (pouched animals). It may be
observed, although no specimens of so high a class of animals as mammalia
are found earlier, such may nevertheless have existed: the defect may be
in our not having found them; but, other things considered, the
probability is that heretofore there were no mammifers. It is an
interesting circumstance that the first mammifers found should have
belonged to the marsupialia, when the place of that order in the scale of
creation is considered. In the imperfect structure of their brain,
deficient in the organs connecting the two hemispheres—and in the mode of
gestation, which is only in small part uterine—this family is clearly a
link between the oviparous vertebrata (birds, reptiles, and fishes) and
the higher mammifers. This is further established by their possessing a
faint development of two canals passing from near the anus to the
external surface of the viscera, which are fully possessed in reptiles
and fishes, for the purpose of supplying aerated water to the blood
circulating in particular vessels, but which are unneeded by mammifers.
Such rudiments of organs in certain species which do not require them in
any degree, are common in both the animal and vegetable kingdoms, but are
always most conspicuous in families approaching in character to those
classes to which the full organs are proper. This subject will be more
particularly adverted to in the sequel.
The highest part of the oolitic formation presents some phenomena of an
unusual and interesting character, which demand special notice.
Immediately above the upper oolitic group in Buckinghamshire, in the
vicinity of Weymouth, and other situations, there is a thin stratum,
usually called by workmen the _dirt-bed_, which appears, from
incontestable evidence, to have been a soil, formed, like soils of the
present day, in the course of time, upon a surface which had previously
been the bottom of the sea. The dirt-bed contains exuviæ of tropical
trees, accumulated through time, as the forest shed its honours on the
spot where it grew, and became itself decayed. Near Weymouth there is a
piece of this stratum, in which stumps of trees remain rooted, mostly
erect or slightly inclined, and from one to three feet high; while trunks
of the same forest, also silicified, lie imbedded on the surface of the
soil in which they grew.
Above this bed lie those which have been called the Wealden, from their
full development in the Weald of Sussex; and these as incontestably argue
that the dry land forming the dirt-bed had next afterwards become the
area of brackish estuaries, or lakes partially connected with the sea;
for the Wealden strata contain exuviæ of fresh-water tribes, besides
those of the great saurians and chelonia. The area of this estuary
comprehends the whole south-east province of England. A geologist thus
confidently narrates the subsequent events: “Much calcareous matter was
first deposited [in this estuary], and in it were entombed myriads of
shells, apparently analogous to those of the vivipara. Then came a thick
envelope of sand, sometimes interstratified with mud; and, finally, muddy
matter prevailed. The solid surface beneath the waters would appear to
have suffered a long continued and gradual depression, which was as
gradually filled, or nearly so, with transported matter; in the end,
however, after a depression of several hundred feet, the sea again
entered upon the area, not suddenly or violently—for the Wealden rocks
pass gradually into the superincumbent cretaceous series—but so quietly,
that the mud containing the remains of terrestrial and fresh-water
creatures was tranquilly covered up by sands replete with marine exuviæ.”
{114} A subsequent depression of the same area, to the depth of at least
three hundred fathoms, is believed to have taken place, to admit of the
deposition of the cretaceous beds lying above.
From the scattered way in which remains of the larger terrestrial animals
occur in the Wealden, and the intermixture of pebbles of the special
appearance of those worn in rivers, it is also inferred that the estuary
which once covered the south-east part of England was the mouth of a
river of that far-descending class of which the Mississippi and Amazon
are examples. What part of the earth’s surface presented the dry land
through which that and other similar rivers flowed, no one can tell for
certain. It has been surmised, that the particular one here spoken of
may have flowed from a point not nearer than the site of the present
Newfoundland. Professor Philips has suggested, from the analogy of the
mineral composition, that anciently elevated coal strata may have
composed the dry land from which the sandy matters of these strata were
washed. Such a deposit as the Wealden almost necessarily implies a
local, not a general condition; yet it has been thought that similar
strata and remains exist in the Pays de Bray, near Beauvais. This leads
to the supposition that there may have been, in that age, a series of
river-receiving estuaries along the border of some such great ocean as
the Atlantic, of which that of modern Sussex is only an example.
ERA OF THE CRETACEOUS FORMATION.
THE record of this period consists of a series of strata, in which chalk
beds make a conspicuous appearance, and which is therefore called the
cretaceous system or formation. In England, a long stripe, extending
from Yorkshire to Kent, presents the cretaceous beds upon the surface,
generally lying conformably upon the oolite, and in many instances rising
into bold escarpments towards the west. The celebrated cliffs of Dover
are of this formation. It extends into northern France, and thence
north-westward into Germany, whence it is traced into Scandinavia and
Russia. The same system exists in North America, and probably in other
parts of the earth not yet geologically investigated. Being a marine
deposit, it establishes that seas existed at the time of its formation on
the tracts occupied by it, while some of its organic remains prove that,
in the neighbourhood of those seas, there were tracts of dry land.
The cretaceous formation in England presents beds chiefly sandy in the
lowest part, chiefly clayey in the middle, and chiefly of chalk in the
upper part, the chalk beds being never absent, which some of the lower
are in several places. In the vale of the Mississippi, again, the true
chalk is wholly, or all but wholly absent. In the south of England, the
lower beds are, (reckoning from the lowest upwards), 1. _Shankland_ or
_greensand_, “a triple alternation of sands and sandstones with clay;” 2.
Galt, “a stiff blue or black clay, abounding in shells, which frequently
possess a pearly lustre;” 3. _Hard_ chalk; 4. Chalk with flints; these
two last being generally white, but in some districts red, and in others
yellow. The whole are, in England, about 1200 feet thick, shewing the
considerable depths of the ocean in which the deposits were made.
Chalk is a carbonate of lime, and the manner of its production in such
vast quantities was long a subject of speculation among geologists. Some
light seemed to be thrown upon the subject a few years ago, when it was
observed, that the detritus of coral reefs in the present tropical seas
gave a powder, undistinguishable, when dried, from ordinary chalk. It
then appeared likely that the chalk beds were the detritus of the corals
which were in the oceans of that era. Mr. Darwin, who made some curious
inquiries on this point, further suggested, that the matter might have
intermediately passed through the bodies of worms and fish, such as feed
on the corals of the present day, and in whose stomachs he has found
impure chalk. This, however, cannot be a full explanation of the
production of chalk, if we admit some more recent discoveries of
Professor Ehrenberg. That master of microscopic investigation announces,
that chalk is composed partly of “inorganic particles of irregular
elliptical structure and granular slaty disposition,” and partly of
shells of inconceivable minuteness, “varying from the one-twelfth to the
two hundred and eighty-eighth part of a line”—a cubic inch of the
substance containing above ten millions of them! The chalk of the north
of Europe contains, he says, a larger proportion of the inorganic matter;
that of the south, a larger proportion of the organic matter, being in
some instances almost entirely composed of it. He has been able to
classify many of these creatures, some of them being allied to the
nautili, nummuli, cyprides, &c. The shells of some are calcareous, of
others siliceous. M. Ehrenberg has likewise detected microscopic
sea-plants in the chalk.
The distinctive feature of the uppermost chalk beds in England, is the
presence of flint nodules. These are generally disposed in layers
parallel to each other. It was readily presumed by geologists that these
masses were formed by a chemical aggregation of particles of silica,
originally held in solution in the mass of the chalk. But whence the
silica in a substance so different from it? Ehrenberg suggests that it
is composed of the siliceous coverings of a portion of the microscopic
creatures, whose shells he has in other instances detected in their
original condition. It is remarkable that the chalk _with_ flint abounds
in the north of Europe; that _without_ flints in the south; while in the
northern chalk siliceous animalcules are wanting, and in the southern
present in great quantities. The conclusion seems but natural, that in
the one case the siliceous exuviæ have been left in their original form;
in the other dissolved chemically, and aggregated on the common principle
of chemical affinity into nodules of flint, probably concentrating, in
every instance, upon a piece of decaying organic matter, as has been the
case with the nodules of ironstone in the earlier rocks, and the
spherules of the oolite.
What is more remarkable, M. Ehrenberg has ascertained that at least
fifty-seven species of the microscopic animals of the chalk, being
infusoria and calcareous-shelled polythalamia, are still found living in
various parts of the earth. These species are the most abundant in the
rock. Singly they are the most unimportant of all animals, but in the
mass, forming as they do such enormous strata over a large part of the
earth’s surface, they have an importance greatly exceeding that of the
largest and noblest of the beasts of the field. Moreover, these species
have a peculiar interest, as the only specific types of that early age
which are reproduced in the present day. Species of sea mollusks, of
reptiles, and of mammifers, have been changed again and again, since the
cretaceous era; and it is not till a long subsequent age that we find the
first traces of any other of even the humblest species which now exist;
but here have these humble infusoria and polythalamia kept their place on
earth through all its revolutions since that time,—are we to say, safe in
their very humility, which might adapt them to a greater variety of
circumstances than most other animals, or are we required to look for
some other explanation of the phenomenon?
All the ordinary and more observable orders of the inhabitants of the
sea, except the cetacea, have been found in the cretaceous
formation—zoophytes, radiaria, mollusks, crustacea, (in great variety of
species,) and fishes in smaller variety. In Europe, remains of the
marine saurians have been found; they may be presumed to have become
extinct in that part of the globe before this time, their place and
destructive office being perhaps supplied by cartilaginous fishes, of
which the teeth are found in great quantities. In America, however,
remains of the plesiosaurus have been discovered in this part of the
stratified series. The reptiles, too, so numerous in the two preceding
periods, appear to have now much diminished in numbers. One, entitled
the mosæsaurus, seems to have held an intermediate place between the
monitor and iguana, and to have been about twenty-five feet long, with a
tail calculated to assist it powerfully in swimming. Crocodiles and
turtles existed, and amongst the fishes were some of a saurian character.
Fuci abounded in the seas of this era. Confervæ are found enclosed in
flints. Of terrestrial vegetation, as of terrestrial animals, the
specimens in the European area are comparatively rare, rendering it
probable that there was no dry land near. The remains are chiefly of
ferns, conifers, and cycadeæ, but in the two former cases we have only
cones and leaves. There have been discovered many pieces of wood,
containing holes drilled by the teredo, and thus shewing that they had
been long drifted about in the ocean before being entombed at the bottom.
The series in America corresponding to this, entitled the ferruginous
sand formation, presents fossils generally identical with those of
Europe, not excepting the fragments of drilled wood; shewing that, in
this, as in earlier ages, there was a parity of conditions for animal
life over a vast tract of the earth’s surface. To European reptiles, the
American formation adds a gigantic one, styled the saurodon, from the
lizard-like character of its teeth.
We have seen that footsteps of birds are considered to have been
discovered in America, in the new red sandstone. Some similar isolated
phenomena occur in the subsequent formations. Mr. Mantell discovered
some bones of birds, apparently waders, in the Wealden. The immediate
connexion of that set of birds with land, may account, of course, for
their containing a terrestrial organic relic, which the marine beds above
and below did not possess. In the slate of Glarus, in Switzerland,
corresponding to the English galt, in the chalk formation, the remains of
a bird have been found. From a chalk bed near Maidstone, have likewise
been extracted some remains of a bird, supposed to have been of the
long-winged swimmer family, and equal in size to the albatross. These,
it must be owned, are less strong traces of the birds than we possess of
the reptiles and other tribes; but it must be remembered, that the
evidence of fossils, as to the absence of any class of animals from a
certain period of the earth’s history, can never be considered as more
than negative. Animals, of which we find no remains in a particular
formation, may, nevertheless, have lived at the time, and it may have
only been from unfavourable circumstances that their remains have not
been preserved for our inspection. The single circumstance of their
being little liable to be carried down into seas, might be the cause of
their non-appearance in our quarries. There is at the same time a limit
to uncertainty on this point. We see, from what remains have been found
in the whole series, a clear progress throughout, from humble to superior
types of being. Hence we derive a light as to what animals may have
existed at particular times, which is in some measure independent of the
specialties of fossilology. The birds are below the mammalia in the
animal scale; and therefore they may be supposed to have existed about
the time of the new red sandstone and oolite, although we find but slight
traces of them in those formations, and, it may be said, till a
considerably later period.
ERA OF THE TERTIARY FORMATION.—
MAMMALIA ABUNDANT.
THE chalk-beds are the highest which extend over a considerable space;
but in hollows of these beds, comparatively limited in extent, there have
been formed series of strata—clays, limestones, marls, alternating—to
which the name of the _Tertiary Formation_ has been applied. London and
Paris alike rest on basins of this formation, and another such basin
extends from near Winchester, under Southampton, and re-appears in the
Isle of Wight. There is a patch, or fragment of the formation in one of
the Hebrides. A stripe of it extends along the east coast of North
America, from Massachusetts to Florida. It is also found in Sicily and
Italy, insensibly blended with formations still in progress. Though
comparatively a local formation, it is not of the less importance as a
record of the condition of the earth during a certain period. As in
other formations, it is marked, in the most distant localities, by
identity of organic remains.
The hollows filled by the tertiary formation must be considered as the
beds of estuaries left at the conclusion of the cretaceous period. We
have seen that an estuary, either by the drifting up of its mouth, or a
change of level in that quarter, may be supposed to have become an inland
sheet of water, and that, by another change, of the reverse kind, it may
be supposed to have become an estuary again. Such changes the Paris
basin appears to have undergone oftener than once, for, first, we have
there a fresh-water formation of clay and limestone beds; then, a
marine-limestone formation; next, a second fresh water formation, in
which the material of the celebrated _plaster of Paris_ (gypsum) is
included; then, a second marine formation of sandy and limy beds; and
finally, a third series of fresh-water strata. Such alternations occur
in other examples of the tertiary formation likewise.
The tertiary beds present all but an entirely new set of animals, and as
we ascend in the series, we find more and more of these identical with
species still existing upon earth, as if we had now reached the dawn of
the present state of the zoology of our planet. By the study of the
shells alone, Mr. Lyell has been enabled to divide the whole term into
four sub-periods, to which he has given names with reference to the
proportions which they respectively present of surviving species—first,
the eocene, (from ’ηως, the dawn; χαινος, recent;) second, the miocene,
(μειων, less;) third, older pliocene, (πλειων, more;) fourth, newer
pliocene.
EOCENE SUB-PERIOD.
The eocene period presents, in three continental groups, 1238 species of
shells, of which forty-two, or 3.5 per cent, yet flourish. Some of these
are remarkable enough; but they all sink into insignificance beside the
mammalian remains which the lower eocene deposits of the Paris basin
present to us, shewing that the land had now become the theatre of an
extensive creation of the highest class of animals. Cuvier ascertained
about fifty species of these, all of them long since extinct. A
considerable number are _pachydermata_, {127} of a character
approximating to the South American tapir: the names, palæotherium,
anthracotherium, anoplotherium, lophiodon, &c., have been applied to them
with a consideration of more or less conspicuous peculiarities; but a
description of the first may give some general idea of the whole. It was
about the size of a horse, but more squat and clumsy, and with a heavier
head, and a lower jaw shorter than the upper; the feet, also, instead of
hooves, presented three large toes, rounded, and unprovided with claws.
These animals were all herbivorous. Amongst an immense number of others
are found many new reptiles, some of them adapted for fresh water;
species of birds allied to the sea-lark, curlew, quail, buzzard, owl, and
pelican; species allied to the dormouse and squirrel; also the opossum
and racoon; and species allied to the genette, fox, and wolf.
MIOCENE SUB-PERIOD.
In the miocene sub-period, the shells give eighteen per cent. of existing
species, shewing a considerable advance from the preceding era, with
respect to the inhabitants of the sea. The advance in the land animals
is less marked, but yet considerable. The predominating forms are still
pachydermatous, and the tapir type continues to be conspicuous. One
animal of this kind, called the _dinotherium_, is supposed to have been
not less than eighteen feet long; it had a mole-like form of the
shoulder-blade, conferring the power of digging for food, and a couple of
tusks turning down from the lower jaw, by which it could have attached
itself, like the walrus, to a shore or bank, while its body floated in
the water. Dr. Buckland considers this and some similar miocene animals,
as adapted for a semi-aquatic life, in a region where lakes abounded.
Besides the tapirs, we have in this era animals allied to the glutton,
the bear, the dog, the horse, the hog, and lastly, several felinæ,
(creatures of which the lion is the type;) all of which are new forms, as
far as we know. There was also an abundance of marine mammalia, seals,
dolphins, lamantins, walruses, and whales, none of which had previously
appeared.
PLIOCENE SUB-PERIOD.
The shells of the older pliocene give from thirty-five to fifty; those of
the newer, from ninety to ninety-five per cent. of existing species. The
pachydermata of the preceding era now disappear, and are replaced by
others belonging to still existing families—elephant, hippopotamus,
rhinoceros—though now extinct as species. Some of these are startling,
from their enormous magnitude. The great mastodon, whose remains are
found in abundance in America, was a species of elephant, judged, from
peculiarities of its teeth, to have lived on aquatic plants, and reaching
the height of twelve feet. The mammoth was another elephant, but
supposed to have survived till comparatively recent times, as a specimen,
in all respects entire, was found in 1801, preserved in ice, in Siberia.
We are more surprised by finding such gigantic proportions in an animal
called the megatherium, which ranks in an order now assuming much humbler
forms—the edentata—to which the sloth, ant-eater, and armadillo belong.
The megatherium had a skeleton of enormous solidity, with an armour-clad
body, and five toes, terminating in huge claws, wherewith to grasp the
branches, from which, like its existing congener, the sloth, it derived
its food. The megalonyx was a similar animal, only somewhat less than
the preceding. Finally, the pliocene gives us for the first time, oxen,
deer, camels, and other specimens of the _ruminantia_.
Such is an outline of the fauna of the tertiary era, as ascertained by
the illustrious naturalists who first devoted their attention to it. It
will be observed that it brings us up to the felinæ, or carnivora, a
considerably elevated point in the animal scale, but still leaving a
blank for the quadrumana (monkeys) and for man, who collectively form, as
will be afterwards seen, the first group in that scale. It sometimes
happens, however, as we have seen, that a few rare traces of a particular
class of animals are in time found in formations originally thought to be
destitute of them, displaying as it were a dawn of that department of
creation. Such seems to be the case with at least the quadrumana. A
jaw-bone and tooth of an animal of this order, and belonging to the genus
macacus, were found in the London clay, (eocene,) at Kyson, near
Woodbridge, in 1839. Another jaw-bone, containing several teeth,
supposed to have belonged to a species of monkey about three feet high,
was discovered about the same time in a stratum of marl surmounted by
compact limestone, in the department of Gers, at the foot of the
Pyrenees. Associated with this last were remains of not less than thirty
mammiferous quadrupeds, including three species of rhinoceros, a large
anoplotherium, three species of deer, two antelopes, a true dog, a large
cat, an animal like a weasel, a small hare, and a huge species of the
edentata. Both of these places are considerably to the north of any
region now inhabited by the monkey tribes. Fossil remains of quadrumana
have been found in at least two other parts of the earth,—namely, the
sub-Himalayan hills, near the Sutlej, and in Brazil, (both in the
tertiary strata;) the first being a large species of semnopithecus, and
the second, a still larger animal belonging to the American group of
monkeys, but a new genus, and denominated by its discoverer, Dr. Lund,
protopithecus. The latter would be four feet in height.
One remarkable circumstance connected with the tertiary formation remains
to be noticed,—namely, the prevalence of volcanic action at that era. In
Auvergne, in Catalonia, near Venice, and in the vicinity of Rome and
Naples, lavas exactly resembling the produce of existing volcanoes, are
associated and intermixed with the lacustrine as well as marine
tertiaries. The superficies of tertiaries in England is disturbed by two
great swells, forming what are called anticlinal axes, one of which
divides the London from the Hampshire basin, while the other passes
through the Isle of Wight, both throwing the strata down at violent
inclination towards the north, as if the subterranean disturbing force
had _waved_ forward in that direction. The Pyrenees, too, and Alps, have
both undergone elevation since the deposition of the tertiaries; and in
Sicily there are mountains which have risen three thousand feet since the
deposition of some of the most recent of these rocks. The general effect
of these operations was of course to extend the land surface, and to
increase the variety of its features, thus improving the natural
drainage, and generally adapting the earth for the reception of higher
classes of animals.
ERA OF THE SUPERFICIAL FORMATIONS.
COMMENCEMENT OF PRESENT SPECIES.
WE have now completed our survey of the series of stratified rocks, and
traced in their fossils the progress of organic creation down to a time
which seems not long antecedent to the appearance of man. There are,
nevertheless, monuments of still another era or space of time which it is
all but certain did also precede that event.
Over the rock formations of all eras, in various parts of the globe, but
confined in general to situations not very elevated, there is a layer of
stiff clay, mostly of a blue colour, mingled with fragments of rock of
all sizes, travel-worn, and otherwise, and to which geologists give the
name of diluvium, as being apparently the produce of some vast flood, or
of the sea thrown into an unusual agitation. It seems to indicate that,
at the time when it was laid down, much of the present dry land was under
the ocean, a supposition which we shall see supported by other evidence.
The included masses of rock have been carefully inspected in many places,
and traced to particular parent beds at considerable distances.
Connected with these phenomena are certain rock surfaces on the slopes of
hills and elsewhere, which exhibit groovings and scratchings, such as we
might suppose would be produced by a quantity of loose blocks hurried
along over them by a flood. Another associated phenomenon is that called
_crag and tail_, which exists in many places,—namely, a rocky mountain,
or lesser elevation, presenting on one side the naked rock in a more or
less abrupt form, and on the other a gentle slope; the sites of Windsor,
Edinburgh, and Stirling, with their respective castles, are specimens of
crag and tail. Finally, we may advert to certain long ridges of clay and
gravel which arrest the attention of travellers on the surface of Sweden
and Finland, and which are also found in the United States, where,
indeed, the whole of these phenomena have been observed over a large
surface, as well as in Europe. It is very remarkable that the direction
from which the diluvial blocks have generally come, the lines of the
grooved rock surfaces, the direction of the crag and tail eminences, and
that of the clay and gravel ridges—phenomena, be it observed, extending
over the northern parts of both Europe and America—are _all from the
north and north-west towards the south-east_. We thus acquire the idea
of a powerful current moving in a direction from north-west to
south-east, carrying, besides mud, masses of rock which furrowed the
solid surfaces as they passed along, abrading the north-west faces of
many hills, but leaving the slopes in the opposite direction uninjured,
and in some instances forming long ridges of detritus along the surface.
These are curious considerations, and it has become a question of much
interest, by what means, and under what circumstances, was such a current
produced. One hypothetical answer has some plausibility about it. From
an investigation of the nature of glaciers, and some observations which
seem to indicate that these have at one time extended to lower levels,
and existed in regions (the Scottish Highlands an example) where there is
now no perennial snow, it has been surmised that there was a time,
subsequent to the tertiary era, when the circumpolar ice extended far
into the temperate zone, and formed a lofty, as well as extensive
accumulation. A change to a higher temperature, producing a sudden thaw
of this mass, might set free such a quantity of water as would form a
large flood, and the southward flow of this deluge, joined to the
direction which it would obtain from the rotatory motion of the globe,
would of course produce that compound or south-easterly direction which
the phenomena require. All of these speculations are as yet far too
deficient in facts to be of much value; and I must freely own that, for
one, I attach little importance to them. All that we can legitimately
infer from the diluvium is, that the northern parts of Europe and America
were then under the sea, and that a strong current set over them.
Connected with the diluvium is the history of _ossiferous caverns_, of
which specimens singly exist at Kirkdale in Yorkshire, Gailenreuth in
Franconia, and other places. They occur in the calcareous strata, as the
great caverns generally do, but have in all instances been naturally
closed up till the recent period of their discovery. The floors are
covered with what appears to be a bed of the diluvial clay, over which
rests a crust of stalagmite, the result of the droppings from the roof
since the time when the clay-bed was laid down. In the instances above
specified, and several others, there have been found, under the clay bed,
assemblages of the bones of animals, of many various kinds. At Kirkdale,
for example, the remains of twenty-four species were ascertained—namely,
pigeon, lark, raven, duck, and partridge; mouse, water-rat, rabbit, hare,
deer, (three species,) ox, horse, hippopotamus, rhinoceros, elephant,
weazel, fox, wolf, bear, tiger, hyena. From many of the bones of the
gentler of these animals being found in a broken state, it is supposed
that the cave was a haunt of hyenas and other predaceous animals, by
which the smaller ones were here consumed. This must have been at a time
antecedent to the submersion which produced the diluvium, since the bones
are covered by a bed of that formation. It is impossible not to see here
a very natural series of incidents. First, the cave is frequented by
wild beasts, who make it a kind of charnel-house. Then, submerged in the
current which has been spoken of, it receives a clay flooring from the
waters containing that matter in suspension. Finally, raised from the
water, but with no mouth to the open air, it remains unintruded on for a
long series of ages, during which the clay flooring receives a new
calcareous covering, from the droppings of the roof. Dr. Buckland, who
examined and described the Kirkdale cave, was at first of opinion that it
presented a physical evidence of the Noachian deluge; but he afterwards
saw reason to consider its phenomena as of a time far apart from that
event, which rests on evidence of an entirely different kind.
Our attention is next drawn to the erratic blocks or boulders, which in
many parts of the earth are thickly strewn over the surface, particularly
in the north of Europe. Some of these blocks are many tons in weight,
yet are clearly ascertained to have belonged originally to situations at
a great distance. Fragments, for example, of the granite of Shap Fell
are found in every direction around to the distance of fifty miles, one
piece being placed high upon Criffel Mountain, on the opposite side of
the Solway estuary; so also are fragments of the Alps found far up the
slopes of the Jura. There are even blocks on the east coast of England,
supposed to have travelled from Norway. The only rational conjecture
which can be formed as to the transport of such masses from so great a
distance, is one which presumes them to have been carried and dropped by
icebergs, while the space between their original and final sites was
under ocean. Icebergs do even now carry off such masses from the polar
coasts, which, falling when the retaining ice melts, must take up
situations at the bottom of the sea analogous to those in which we find
the erratic blocks of the present day.
As the diluvium and erratic blocks clearly suppose one last long
submersion of the surface, (_last_, geologically speaking,) there is
another set of appearances which as manifestly shew the steps by which
the land was made afterwards to reappear. These consist of _terraces_,
which have been detected near, and at some distance inland from, the
coast lines of Scandinavia, Britain, America, and other regions; being
evidently ancient beaches, or platforms, on which the margin of the sea
at one time rested. They have been observed at different heights above
the present sea-level, from twenty to above twelve hundred feet; and in
many places they are seen rising above each other in succession, to the
number of three, four, and even more. The smooth flatness of these
terraces, with generally a slight inclination towards the sea, the sandy
composition of many of them, and, in some instances, the preservation of
marine shells in the ground, identify them perfectly with existing
sea-beaches, notwithstanding the cuts and scoopings which have every here
and there been effected in them by water-courses. The irresistible
inference from the phenomena is, that the highest was first the coast
line; then an elevation took place, and the second highest became so, the
first being now raised into the air and thrown inland. Then, upon
another elevation, the sea began to form, at its new point of contact
with the land, the third highest beach, and so on down to the platform
nearest to the present sea-beach. Phenomena of this kind become
comparatively familiar to us, when we hear of evidence that the last
sixty feet of the elevation of Sweden, and the last eighty-five of that
of Chili, have taken place since man first dwelt in those countries; nay,
that the elevation of the former country goes on at this time at the rate
of about forty-five inches in a century, and that a thousand miles of the
Chilian coast rose four feet in one night, under the influence of a
powerful earthquake, so lately as 1822. Subterranean forces, of the kind
then exemplified in Chili, supply a ready explanation of the whole
phenomena, though some other operating causes have been suggested. In an
inquiry on this point, it becomes of consequence to learn some
particulars respecting the levels. Taking a particular beach, it is
generally observed that the level continues the same along a considerable
number of miles, and nothing like breaks or hitches has as yet been
detected in any case. A second and a third beach are also observed to be
exactly parallel to the first. These facts would seem to indicate quiet
elevating movements, uniform over a large tract. It must, however, be
remarked that the raised beaches at one part of a coast rarely coincide
with those at another part forty or fifty miles off. We might suppose
this to indicate a limit in that extent of the uniformity of the
elevating cause, but it would be rash to conclude positively that such is
the case. In the present sea, as is well known, there are different
levels at different places, owing to the operation of peculiar local
causes, as currents, evaporation, and the influx of large rivers into
narrow-mouthed estuaries. The differences of level in the ancient
beaches might be occasioned by some such causes. But, whatever doubt may
rest on this minor point, enough has been ascertained to settle the main
one, that we have in these platforms indubitable monuments of the last
rise of the land from the sea, and the concluding great event of the
geological history.
The idea of such a wide-spread and possibly universal submersion
unavoidably suggests some considerations as to the effect which it might
have upon terrestrial animal life. It seems likely that this would be,
on such an occasion, extensively, if not universally destroyed. Nor does
the idea of its universal destruction seem the less plausible, when we
remark, that none of the species of land animals heretofore discovered
can be detected at a subsequent period. The whole seem to have been now
changed. Some geologists appear much inclined to think that there was at
this time a new development of terrestrial animal life upon the globe,
and M. Agassiz, whose opinion on such a subject must always be worthy of
attention, speaks all but decidedly for such a conclusion. It must,
however, be owned, that proofs for it are still scanty, beyond the bare
fact of a submersion which appears to have had a very wide range. I must
therefore be content to leave this point, as far as geological evidence
is concerned, for future affirmation.
There are some other superficial deposits, of less consequence on the
present occasion than the diluvium—namely, lacustrine deposits, or
filled-up lakes; alluvium, or the deposits of rivers beside their
margins; deltas, the deposits made by great ones at their efflux into the
sea; peat mosses; and the vegetable soil. The animal remains found in
these generally testify to a zoology on the verge of that which still
exists, or melting into it, there being included many species which still
exist. In a lacustrine deposit at Market-Weighton, in the Vale of York,
there have been found bones of the elephant, rhinoceros, bison, wolf,
horse, felis, deer, birds, all or nearly all extinct species; associated
with thirteen species of land and fresh water shells, “exactly identical
with types now living in the vicinity.” In similar deposits in North
America, are remains of the mammoth, mastodon, buffalo, and other animals
of extinct and living types. In short, these superficial deposits shew
precisely such remains as might be expected from a time at which the
present system of things (to use a vague but not unexpressive phrase)
obtained, but yet so far remote in chronology as to allow of the dropping
of many species, through familiar causes, in the interval. Still,
however, there is no authentic or satisfactory instance of human remains
being found, except in deposits obviously of very modern date; a
tolerably strong proof that the creation of our own species is a
comparatively recent event, and one posterior (generally speaking) to all
the great natural transactions chronicled by geology.
GENERAL CONSIDERATIONS
RESPECTING
THE ORIGIN OF THE ANIMATED TRIBES.
THUS concludes the wondrous chapter of the earth’s history which is told
by geology. It takes up our globe at the period when its original
incandescent state had nearly ceased; conducts it through what we have
every reason to believe were vast, or at least very considerable, spaces
of time, in the course of which many superficial changes took place, and
vegetable and animal life was gradually developed; and drops it just at
the point when man was apparently about to enter on the scene. The
compilation of such a history, from materials of so extraordinary a
character, and the powerful nature of the evidence which these materials
afford, are calculated to excite our admiration, and the result must be
allowed to exalt the dignity of science, as a product of man’s industry
and his reason.
If there is any thing more than another impressed on our minds by the
course of the geological history, it is, that the same laws and
conditions of nature now apparent to us have existed throughout the whole
time, though the operation of some of these laws may now be less
conspicuous than in the early ages, from some of the conditions having
come to a settlement and a close. That seas have flowed and ebbed, and
winds disturbed their surfaces, in the time of the secondary rocks, we
have proof on the yet preserved surfaces of the sands which constituted
margins of the seas in those days. Even the fall of wind-slanted rain is
evidenced on the same tablets. The washing down of detached matter from
elevated grounds, which we see rivers constantly engaged in at the
present time, and which is daily shallowing the seas adjacent to their
mouths, only appears to have proceeded on a greater scale in earlier
epochs. The volcanic subterranean force, which we see belching forth
lavas on the sides of mountains, and throwing up new elevations by land
and sea, was only more powerfully operative in distant ages. To turn to
organic nature, vegetation seems to have proceeded then exactly as now.
The very alternations of the seasons has been read in unmistakable
characters in sections of the trees of those days, precisely as it might
be read in a section of a tree cut down yesterday. The system of prey
amongst animals flourished throughout the whole of the pre-human period;
and the adaptation of all plants and animals to their respective spheres
of existence was as perfect in those early ages as it is still.
But, as has been observed, the operation of the laws may be modified by
conditions. At one early age, if there was any dry land at all, it was
perhaps enveloped in an atmosphere unfit for the existence of terrestrial
animals, and which had to go though some changes before that condition
was altered. In the carbonigenous era, dry land seems to have consisted
only of clusters of islands, and the temperature was much above what now
obtains at the same places. Volcanic forces, and perhaps also the
disintegrating power, seem to have been on the decrease since the first,
or we have at least long enjoyed an exemption from such paroxysms of the
former, as appear to have prevailed at the close of the coal formation in
England and throughout the tertiary era. The surface has also undergone
a gradual progress by which it has become always more and more
variegated, and thereby fitted for the residence of a higher class of
animals.
In pursuing the progress of the development of both plants and animals
upon the globe, we have seen an advance in both cases, along the line
leading to the higher forms of organization. Amongst plants, we have
first sea-weeds, afterwards land plants; and amongst these the simpler
(cellular and cryptogamic) before the more complex. In the department of
zoology, we see zoophytes, radiata, mollusca, articulata, existing for
ages before there were any higher forms. The first step forward gives
fishes, the humblest class of the vertebrata; and, moreover, the earliest
fishes partake of the character of the next lowest sub-kingdom, the
articulata. Afterwards come land animals, of which the first are
reptiles, universally allowed to be the type next in advance from fishes,
and to be connected with these by the links of an insensible gradation.
From reptiles we advance to birds, and thence to mammalia, which are
commenced by marsupialia, acknowledgedly low forms in their class. That
there is thus a progress of some kind, the most superficial glance at the
geological history is sufficient to convince us. Indeed the doctrine of
the gradation of animal forms has received a remarkable support from the
discoveries of this science, as several types formerly wanting to a
completion of the series have been found in a fossil state. {149}
It is scarcely less evident, from the geological record, that the
progress of organic life has observed some correspondence with the
progress of physical conditions on the surface. We do not know for
certain that the sea, at the time when it supported radiated, molluscous,
and articulated families, was incapable of supporting fishes; but causes
for such a limitation are far from inconceivable. The huge saurians
appear to have been precisely adapted to the low muddy coasts and sea
margins of the time when they flourished. Marsupials appear at the time
when the surface was generally in that flat, imperfectly variegated state
in which we find Australia, the region where they now live in the
greatest abundance, and one which has no higher native mammalian type.
Finally, it was not till the land and sea had come into their present
relations, and the former, in its principal continents, had acquired the
irregularity of surface necessary for man, that man appeared. We have
likewise seen reason for supposing that land animals could not have lived
before the carbonigenous era, owing to the great charge of carbonic acid
gas presumed to have been contained in the atmosphere down to that time.
The surplus of this having gone, as M. Brogniart suggests, to form the
vegetation, whose ruins became coal, and the air being thus brought to
its present state, land animals immediately appeared. So also,
sea-plants were at first the only specimens of vegetation, because there
appears to have been no place where other plants could be produced or
supported. Land vegetation followed, at first simple, afterwards
complex, probably in conformity with an advance of the conditions
required by the higher class of plants. In short, we see everywhere
throughout the geological history, strong traces of a parallel advance of
the physical conditions and the organic forms.
In examining the fossils of the lower marine creation, with a reference
to the kind of rock in connexion, with which they are found, it is
observed that some strata are attended by a much greater abundance of
both species and individuals than others. They abound most in calcareous
rocks, which is precisely what might be expected, since lime is necessary
for the formation of the shells of the mollusks and articulata, and the
hard substance of the crinoidea and corals; next in the carboniferous
series; next in the tertiary; next in the new red sandstone; next in
slates; and lastly, least of all, in the primary rocks. {151} This may
have been the case without regard to the origination of new species, but
more probably it was otherwise; or why, for instance, should the
polypiferous zoophyta be found almost exclusively in the limestones?
There are, indeed, abundant appearances as if, throughout all the changes
of the surface, the various kinds of organic life invariably _pressed
in_, immediately on the specially suitable conditions arising, so that no
place which could support any form of organic being might be left for any
length of time unoccupied. Nor is it less remarkable how various species
are withdrawn from the earth, when the proper conditions for their
particular existence are changed. The trilobite, of which fifty species
existed during the earlier formations, was extirpated before the
secondary had commenced, and appeared no more. The ammonite does not
appear above the chalk. The species, and even genera of all the early
radiata and mollusks were exchanged for others long ago. Not one species
of any creature which flourished before the tertiary (Ehrenberg’s
infusoria excepted) now exists; and of the mammalia which arose during
that series, many forms are altogether gone, while of others we have now
only kindred species. Thus to find not only frequent additions to the
previously existing forms, but frequent withdrawals of forms which had
apparently become inappropriate—a constant shifting as well as advance—is
a fact calculated very forcibly to arrest attention.
A candid consideration of all these circumstances can scarcely fail to
introduce into our minds a somewhat different idea of organic creation
from what has hitherto been generally entertained. That God created
animated beings, as well as the terraqueous theatre of their being, is a
fact so powerfully evidenced, and so universally received, that I at once
take it for granted. But in the particulars of this so highly supported
idea, we surely here see cause for some re-consideration. It may now be
inquired,—In what way was the creation of animated beings effected? The
ordinary notion may, I think, be not unjustly described as this,—that the
Almighty author produced the progenitors of all existing species by some
sort of personal or immediate exertion. But how does this notion comport
with what we have seen of the gradual advance of species, from the
humblest to the highest? How can we suppose an immediate exertion of
this creative power at one time to produce zoophytes, another time to add
a few marine mollusks, another to bring in one or two conchifers, again
to produce crustaceous fishes, again perfect fishes, and so on to the
end? This would surely be to take a very mean view of the Creative
Power—to, in short, anthropomorphize it, or reduce it to some such
character as that borne by the ordinary proceedings of mankind. And yet
this would be unavoidable; for that the organic creation was thus
progressive through a long space of time, rests on evidence which nothing
can overturn or gainsay. Some other idea must then be come to with
regard to _the mode_ in which the Divine Author proceeded in the organic
creation. Let us seek in the history of the earth’s formation for a new
suggestion on this point. We have seen powerful evidence, that the
construction of this globe and its associates, and inferentially that of
all the other globes of space, was the result, not of any immediate or
personal exertion on the part of the Deity, but of natural laws which are
expressions of his will. What is to hinder our supposing that the
organic creation is also a result of natural laws, which are in like
manner an expression of his will? More than this, the fact of the
cosmical arrangements being an effect of natural laws is a powerful
argument for the organic arrangements being so likewise, for how can we
suppose that the august Being who brought all these countless worlds into
form by the simple establishment of a natural principle flowing from his
mind, was to interfere personally and specially on every occasion when a
new shell-fish or reptile was to be ushered into existence on _one_ of
these worlds? Surely this idea is too ridiculous to be for a moment
entertained.
It will be objected that the ordinary conceptions of Christian nations on
this subject are directly derived from Scripture, or, at least, are in
conformity with it. If they were clearly and unequivocally supported by
Scripture, it may readily be allowed that there would be a strong
objection to the reception of any opposite hypothesis. But the fact is,
however startling the present announcement of it may be, that the first
chapter of the Mosaic record is not only not in harmony with the ordinary
ideas of mankind respecting cosmical and organic creation, but is opposed
to them, and only in accordance with the views here taken. When we
carefully peruse it with awakened minds, we find that all the procedure
is represented primarily and pre-eminently as flowing _from commands and
expressions of will_, _not from direct acts_. Let there be light—let
there be a firmament—let the dry land appear—let the earth bring forth
grass, the herb, the tree—let the waters bring forth the moving creature
that hath life—let the earth bring forth the living creature after his
kind—these are the terms in which the principal acts are described. The
additional expressions,—God made the firmament—God made the beast of the
earth, &c., occur subordinately, and only in a few instances; they do not
necessarily convey a different idea of the mode of creation, and indeed
only appear as alternative phrases, in the usual duplicative manner of
Eastern narrative. Keeping this in view, the words used in a subsequent
place, “God _formed_ man in his own image,” cannot well be understood as
implying any more than what was implied before,—namely, that man was
produced in consequence of an expression of the Divine will to that
effect. Thus, the scriptural objection quickly vanishes, and the
prevalent ideas about the organic creation appear only as a mistaken
inference from the text, formed at a time when man’s ignorance prevented
him from drawing therefrom a just conclusion. At the same time, I freely
own that I do not think it right to adduce the Mosaic record, either in
objection to, or support of any natural hypothesis, and this for many
reasons, but particularly for this, that there is not the least
appearance of an intention in that book to give philosophically exact
views of nature.
To a reasonable mind the Divine attributes must appear, not diminished or
reduced in any way, by supposing a creation by law, but infinitely
exalted. It is the narrowest of all views of the Deity, and
characteristic of a humble class of intellects, to suppose him acting
constantly in particular ways for particular occasions. It, for one
thing, greatly detracts from his foresight, the most undeniable of all
the attributes of Omnipotence. It lowers him towards the level of our
own humble intellects. Much more worthy of him it surely is, to suppose
that all things have been commissioned by him from the first, though
neither is he absent from a particle of the current of natural affairs in
one sense, seeing that the whole system is continually supported by his
providence. Even in human affairs, if I may be allowed to adopt a
familiar illustration, there is a constant progress from specific action
for particular occasions, to arrangements which, once established, shall
continue to answer for a great multitude of occasions. Such plans the
enlightened readily form for themselves, and conceive as being adopted by
all who have to attend to a multitude of affairs, while the ignorant
suppose every act of the greatest public functionary to be the result of
some special consideration and care on his part alone. Are we to suppose
the Deity adopting plans which harmonize only with the modes of procedure
of the less enlightened of our race? Those who would object to the
hypothesis of a creation by the intervention of law, do not perhaps
consider how powerful an argument in favour of the existence of God is
lost by rejecting this doctrine. When all is seen to be the result of
law, the idea of an Almighty Author becomes irresistible, for the
creation of a law for an endless series of phenomena—an act of
intelligence above all else that we can conceive—could have no other
imaginable source, and tells, moreover, as powerfully for a sustaining as
for an originating power. On this point a remark of Dr. Buckland seems
applicable: “If the properties adopted by the elements at the moment of
their creation adapted them beforehand to the infinity of complicated
useful purposes which they have already answered, and may have still
farther to answer, under many dispensations of the material world, such
an aboriginal constitution, so far from superseding an intelligent agent,
would only exalt our conceptions of the consummate skill and power that
could comprehend such an infinity of future uses under future systems, in
the original groundwork of his creation.”
A late writer, in a work embracing a vast amount of miscellaneous
knowledge, but written in a dogmatic style, argues at great length for
the doctrine of more immediate exertions on the part of the Deity in the
works of his creation. One of the most striking of his illustrations is
as follows:—“The coral polypi, united by a common animal bond, construct
a defined form in stone; many kinds construct many forms. An allotted
instinct may permit each polypus to construct its own cell, but there is
no superintending one to direct the pattern, nor can the workers unite by
consultation for such an end. There is no recipient for an instinct by
which the pattern might be constructed. It is God alone, therefore, who
is the architect; and for this end, consequently, he must dispose of
every new polypus required to continue the pattern, in a new and peculiar
position, which the animal could not have discovered by itself. Yet
more, millions of these blind workers unite their works to form an
island, which is also wrought out according to a constant general
pattern, and of a very peculiar nature, though the separate coral works
are numerously diverse. Still less, then, here is an instinct possible.
The Great Architect himself must execute what he planned, in each case
equally. He uses these little and senseless animals as hands; but they
are hands which himself must direct. He must direct each one everywhere,
and therefore he is ever acting.” {159} This is a most notable example
of a dangerous kind of reasoning. It is now believed that corals have a
general life and sensation throughout the whole mass, residing in the
nervous tissue which envelops them; consequently, there is nothing more
wonderful in their determinate general forms than in those of other
animals.
It may here be remarked that there is in our doctrine that harmony in all
the associated phenomena which generally marks great truths. First, it
agrees, as we have seen, with the idea of planet-creation by natural law.
Secondly, upon this supposition, all that geology tells us of the
succession of species appears natural and intelligible. Organic life
_presses in_, as has been remarked, wherever there was room and
encouragement for it, the forms being always such as suited the
circumstances, and in a certain relation to them, as, for example, where
the limestone-forming seas produced an abundance of corals, crinoidea,
and shell-fish. Admitting for a moment a re-origination of species after
a cataclysm, as has been surmised by some geologists, though the
hypothesis is always becoming less and less tenable, it harmonizes with
nothing so well as the idea of a creation by law. The more solitary
commencements of species, which would have been the most inconceivably
paltry exercise for an immediately creative power, are sufficiently
worthy of one operating by laws.
It is also to be observed, that the thing to be accounted for is not
merely the origination of organic being upon this little planet, third of
a series which is but one of hundreds of thousands of series, the whole
of which again form but one portion of an apparently infinite
globe-peopled space, where all seems analogous. We have to suppose, that
every one of these numberless globes is either a theatre of organic
being, or in the way of becoming so. This is a conclusion which every
addition to our knowledge makes only the more irresistible. Is it
conceivable, as a fitting mode of exercise for creative intelligence,
that it should be constantly moving from one sphere to another, to form
and plant the various species which may be required in each situation at
particular times? Is such an idea accordant with our general conception
of the dignity, not to speak of the power, of the Great Author? Yet such
is the notion which we must form, if we adhere to the doctrine of special
exercise. Let us see, on the other hand, how the doctrine of a creation
by law agrees with this expanded view of the organic world.
Unprepared as most men may be for such an announcement, there can be no
doubt that we are able, in this limited sphere, to form some satisfactory
conclusions as to the plants and animals of those other spheres which
move at such immense distances from us. Suppose that the first persons
of an early nation who made a ship and ventured to sea in it, observed,
as they sailed along, a set of objects which they had never before
seen—namely, a fleet of other ships—would they not have been justified in
supposing that those ships were occupied, like their own, by human beings
possessing hands to row and steer, eyes to watch the signs of the
weather, intelligence to guide them from one place to another—in short,
beings in all respects like themselves, or only shewing such differences
as they knew to be producible by difference of climate and habits of
life. Precisely in this manner we can speculate on the inhabitants of
remote spheres. We see that matter has originally been diffused in one
mass, of which the spheres are portions. Consequently, inorganic matter
must be presumed to be everywhere the same, although probably with
differences in the proportions of ingredients in different globes, and
also some difference of conditions. Out of a certain number of the
elements of inorganic matter are composed organic bodies, both vegetable
and animal; such must be the rule in Jupiter and in Sirius, as it is
here. We, therefore, are all but certain that herbaceous and ligneous
fibre, that flesh and blood, are the constituents of the organic beings
of all those spheres which are as yet seats of life. Gravitation we see
to be an all-pervading principle: therefore there must be a relation
between the spheres and their respective organic occupants, by virtue of
which they are fixed, as far as necessary, on the surface. Such a
relation, of course, involves details as to the density and elasticity of
structure, as well as size, of the organic tenants, in proportion to the
gravity of the respective planets—peculiarities, however, which may quite
well consist with the idea of a universality of general types, to which
we are about to come. Electricity we also see to be universal; if,
therefore, it be a principle concerned in life and in mental action, as
science strongly suggests, life and mental action must everywhere be of
one general character. We come to comparatively a matter of detail, when
we advert to heat and light; yet it is important to consider that these
are universal agents, and that, as they bear marked relations to organic
life and structure on earth, they may be presumed to do so in other
spheres also. The considerations as to light are particularly
interesting, for, on our globe, the structure of one important organ,
almost universally distributed in the animal kingdom, is in direct and
precise relation to it. Where there is light there will be eyes, and
these, in other spheres, will be the same in all respects as the eyes of
tellurian animals, with only such differences as may be necessary to
accord with minor peculiarities of condition and of situation. It is but
a small stretch of the argument to suppose that, one conspicuous organ of
a large portion of our animal kingdom being thus universal, a parity in
all the other organs—species for species, class for class, kingdom for
kingdom—is highly likely, and that thus the inhabitants of all the other
globes of space bear not only a general, but a particular resemblance to
those of our own.
Assuming that organic beings are thus spread over all space, the idea of
their having all come into existence by the operation of laws everywhere
applicable, is only conformable to that principle, acknowledged to be so
generally visible in the affairs of Providence, to have all done by the
employment of the smallest possible amount of means. Thus, as one set of
laws produced all orbs and their motions and geognostic arrangements, so
one set of laws overspread them all with life. The whole productive or
creative arrangements are therefore in perfect unity.
PARTICULAR CONSIDERATIONS
RESPECTING
THE ORIGIN OF THE ANIMATED TRIBES.
THE general likelihood of an organic creation by law having been shewn,
we are next to inquire if science has any facts tending to bring the
assumption more nearly home to nature. Such facts there certainly are;
but it cannot be surprising that they are comparatively few and
scattered, when we consider that the inquiry is into one of nature’s
profoundest mysteries, and one which has hitherto engaged no direct
attention in almost any quarter.
Crystallization is confessedly a phenomenon of inorganic matter; yet the
simplest rustic observer is struck by the resemblance which the examples
of it left upon a window by frost bear to vegetable forms. In some
crystallizations the mimicry is beautiful and complete; for example, in
the well-known one called the _Arbor Dianæ_. An amalgam of four parts of
silver and two of mercury being dissolved in nitric acid, and water equal
to thirty weights of the metals being added, a small piece of soft
amalgam of silver suspended in the solution, quickly gathers to itself
the particles of the silver of the amalgam, which form upon it a
_crystallization precisely resembling a shrub_. The experiment may be
varied in a way which serves better to detect the influence of
electricity in such operations, as noted below. {166} Vegetable figures
are also presented in some of the most ordinary appearances of the
electric fluid. In the marks caused by positive electricity, or which it
leaves in its passage, we see the ramifications of a tree, as well as of
its individual leaves; those of the negative, recal the bulbous or the
spreading root, according as they are clumped or divergent. These
phenomena seem to say that the electric energies have had something to do
in determining the forms of plants. That they are intimately connected
with vegetable life is indubitable, for germination will not proceed in
water charged with negative electricity, while water charged positively
greatly favours it; and a garden sensibly increases in luxuriance, when a
number of conducting rods are made to terminate in branches over its
beds. With regard to the resemblance of the ramifications of the
branches and leaves of plants to the traces of the positive electricity,
and that of the roots to the negative, it is a circumstance calling for
especial remark, that the atmosphere, particularly its lower strata, is
generally charged positively, while the earth is always charged
negatively. The correspondence here is curious. A plant thus appears as
a thing formed on the basis of a natural electrical operation—the _brush_
realized. We can thus suppose the various forms of plants as,
immediately, the result of a law in electricity variously affecting them
according to their organic character, or respective germinal
constituents. In the poplar, the brush is unusually vertical, and little
divergent; the reverse in the beech: in the palm, a pencil has proceeded
straight up for a certain distance, radiates there, and turns outwards
and downwards; and so on. We can here see at least traces of secondary
means by which the Almighty Deviser might establish all the vegetable
forms with which the earth is overspread.
Vegetable and animal bodies are mainly composed of the same four simple
substances or elements—carbon, oxygen, hydrogen, and nitrogen. The first
combinations of these in animals are into what are called proximate
principles, as albumen, fibrin, urea, alantoin, &c., out of which the
structure of the animal body is composed. Now the chemist, by the
association of two parts oxygen, four hydrogen, two carbon, and two
nitrogen, can _make urea_. Alantoin has also been produced artificially.
Two of the proximate principles being realizable by human care, the
possibility of realizing or forming all is established. Thus the chemist
may be said to have it in his power to realize the first step in
organization. {169a} Indeed, it is fully acknowledged by Dr. Daubeny,
that in the combinations forming the proximate principles there is no
chemical peculiarity. “It is now certain,” he says, “that the same
simple laws of composition pervade the whole creation; and that, if the
organic chemist only takes the requisite precautions to avoid resolving
into their ultimate elements the proximate principles upon which he
operates, the results of his analysis will shew that they are combined
precisely according to the same plan as the elements of mineral bodies
are known to be.” {169b} A particular fact is here worthy of attention.
“The conversion of fecula into sugar, as one of the ordinary processes of
vegetable economy, is effected by the production of a secretion termed
_diastose_, which occasions both the rupture of the starch vesicles, and
the change of their contained gum into sugar. This diastose may be
separately obtained by the chemist, and it acts as effectually in his
laboratory as in the vegetable organization. He can also imitate its
effects by other chemical agents.” {170} The writer quoted below adds,
“No reasonable ground has yet been adduced for supposing that, if we had
the power of bringing together the elements of any organic compound, in
their requisite states and proportions, the result would be any other
than that which is found in the living body.”
It is much to know the elements out of which organic bodies are composed.
It is something more to know their first combinations, and that these are
simply chemical. How these combinations are associated in the structure
of living bodies is the next inquiry, but it is one to which as yet no
satisfactory answer can be given. The investigation of the minutiæ of
organic structure by the microscope is of such recent origin, that its
results cannot be expected to be very clear. Some facts, however, are
worthy of attention with regard to the present inquiry. It is
ascertained that the basis of all vegetable and animal substances
consists of nucleated cells; that is, cells having granules within them.
Nutriment is converted into these before being assimilated by the system.
The tissues are formed from them. The ovum destined to become a new
creature, is originally only a cell with a contained granule. We see it
acting this reproductive part in the simplest manner in the cryptogamic
plants. “The parent cell, arrived at maturity by the exercise of its
organic functions, bursts, and liberates its contained granules. These,
at once thrown upon their own resources, and entirely dependent for their
nutrition on the surrounding elements, develop themselves into new cells,
which repeat the life of their original. Amongst the higher tribes of
the cryptogamia, the reproductive cell does not burst, but the first
cells of the new structure are developed within it, and these gradually
extend, by a similar process of multiplication, into that primary
leaf-like expansion which is the first formed structure in all plants.”
{171} _Here the little cell becomes directly a plant_, _the full formed
living being_. It is also worthy of remark that, in the sponges, (an
animal form,) a gemmule det
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