CONCERNING CERTAIN PETRIFIED ZOOPHYTES, NOW GENERALLY SUPPOSED
TO BE EXTINCT.
The petrifaction of an animal form or structure has always appeared to
me a most singular process in Nature. The change of such substances as
cellular tissue, or fish-bone, or cartilage, or a light, leathery skin,
into minerals such as silex and agate, seems at first like magic. Scott,
when describing the “foliaged tracery” in the east oriel of Melrose
Abbey, tells his reader:
“Thou wouldst have thought some fairy’s hand
’Twixt poplars straight the osier wand
In many a freakish knot had twined,
Then framed a spell when the work was done,
And changed the willow wreaths to stone.”
But there is no magic in Nature; and when we meet with undoubted
phenomena, however strange they may appear, in any department of her
realm, we must behave ourselves like matter-of-fact persons and set
about accounting for them logically. In a genuine petrifaction there
are two ways of doing this, or, in other words, there are two different
modes in which Nature may have acted so as to produce the result which
we are considering. One of these is that of a simple _substitution_; the
particles of one substance being gradually removed, and those of another
taking their place. This must have been the process which obtained in
many well-known instances: as, for example, when the thin, leathery shell
or husk of an echinus is found perfectly rendered, both as to its general
outline and minute markings, in solid flint or limestone. We feel quite
sure that the original husk has perished; but here is its second self.
The other mode is that of actual _transmutation_, wherein no part
of the original substance is destroyed or removed, but its physical
conditions undergo a total change, by means of either infiltration,
or crystallization, or perhaps both of them combined. This process
has obtained in such cases as a petrified shark’s tooth, or a fossil
trilobite from the Wenlock.
The tooth, which was once bone, is now a kind of metallic stone: the
trilobite once, as we suppose, shell and cartilage, is now a something
between limestone and cast-iron. And this change is very wonderful; but,
as was said above, there is no magic in it, no more than in the hardening
of an infant’s skull, or the solidifying of the arm and leg-bones by the
absorption of phosphate of lime. Besides, the stone and metal now present
are still something different from what we ordinarily mean by those
terms: the petrified tooth is not like a flint-stone, neither could you
cut horse-shoe nails out of the trilobite.
In fact, every _real_ process has a character of its own: a something
which distinguishes it from any other, despite of general resemblances up
to a certain point.
Petrifaction, then, being assumed, as an operation which has really taken
place after one way or another, it falls next to be considered, what
was the original nature of these fossils? I mean the objects which we
find thus preserved in our seaside pebbles. What was the department in
Creation to which they belonged? Was it _animal_ or _vegetable_ before it
thus became altogether _mineral_?
For myself, I will at once say that I have no doubt it was animal; but
not an animal of a very high order. The specimens which I now possess,
and which are all of them chosen, some of them _rare_, I should assign
to such creatures as the “zoophytes” or “polyps,” both radiated and
globular. And I know of nothing, among many hundreds of specimens
gathered from a dozen different beaches, which presents the evidence of
having belonged to vegetable organization, with the exception of sundry
varieties of petrified wood, which speak for themselves, and could not be
mistaken by anybody.
I will now state two or three reasons, which to my own mind are
conclusive, for the above decision.
In the first place, then, the structures here perpetuated in stone are
of great delicacy, and they have been immersed in ancient seas, as is
testified by the localities in which they are obtained. Now vegetable
structure as fine as this, if immersed long enough for any such change
to come in question, must have utterly perished by maceration, and then
the petrifaction could not have taken place. I know that part of the
stem (and I think fruit) of one species of “conifer” has been found in
the Isle of Wight in the condition of a fossil; but this belonged to a
hardy class of plants, and the lobes or plates which composed its bark
and husk are themselves highly siliceous, to say nothing of the presence
of iron in the rind of most of these stems. So that the process would be
a long one, and the fibrous material of the tree would stand it well. But
in these pebbles some of the threads or tubes run from the size of small
twine to that of the rays in a spider’s web; and no vegetable substance
with which I am acquainted, excepting the filaments of “asbestos” (which
is a vegetating _mineral_) in rock-crystal, could abide and retain its
form, so as to allow of the changes by infiltration or otherwise which
have passed upon the original structure.
If it be said in reply to this, that we have the exquisitely delicate
“dendritic” markings, as of leaves and filaments of shrubs or sea-weed,
in the heart of the white chalcedony “mocha-stones” from the East, the
answer is evident: these are not _really_ vegetable traces, but only
_resemble_ such in their configuration and colours. They are simply
shoots and ramifications of a metal,—as iron or manganese. Those in the
“weed-agate” of India, which exactly resemble sprays of fine sea-weed,
are produced by “delessite.”
Indeed, it is both diverting and instructive to observe how Nature
permits, and even seems to abound in, curious coincidences and striking
resemblances between things of entirely diverse character. The dried
polyp, called “encrinoid echinoderm,” bears a wonderful likeness to one
species of Indian corn. (See the plate at p. 137 of Mr. Rymer Jones’s
beautiful work on “The Animal Kingdom.”) And the other day, when I was
enjoying a leisure hour in the British Museum, I suddenly remarked that
the “carapace” (back-shell) of the splendid fossil specimen of the
“Holoptychius nobilissimus” in one of the cases might serve for a sketch
of the back of a _capercailzie_, where the grey and purple feathers
overlap one another. Yet here is no _real_ connection whatever. Only Dame
Nature had gone to play.
_Secondly._ The preservation of these “polyp” forms, in the manner in
which they _have_ been preserved, seems to me to be due to a feature
or circumstance which is strictly animal and not vegetable. I refer to
the fact of the creature, while it was alive, _inhabiting a house_, a
house built by himself, or emanating from his own substance. For, just
as we could know but little of the existence or habits of “shell-fish,”
were it not for their _shells_, so I think we may assume that the
_choanite_ must, when alive, have dwelt in a tough, horny “coperculum,”
answering to the shape of his body and the number of his “polyps” (if
he was a _compound_ creature), because otherwise he would have been
like a jelly-fish or naked slug, and his “polypary” could not have been
preserved in a stony fossil. Of course, whatever was merely flesh,
or adipose matter, has long since perished; but the _house_ or shell
in which it whilome dwelt remains. Thus, the “echinus” built himself
a _dome_, such a residence as a _hedgehog_ would require to live
comfortably in, and through the various orifices of which his spines
could be protruded at pleasure. The “ammonite,” being shaped like a
_snake_, preferred living in a shell of that form, where the creature
when coiled up was safe. The “alcyonite” had a more exquisite taste in
house-building, answering, we may be sure, to the complex and beautiful
structure with which the great Creator had endowed him. His home was a
palace, containing long galleries and secret doors and wheel-windows; and
here some of the delicate tubes are fringed at their extremities like the
petals of a flower.
The antiquity of these formations may be very great, we can scarcely
tell how far removed from our own era. For, while the zoophyte itself is
of a perishable nature, we are acquainted with no substance more durable
(if we except the gems) than that calcareous matter of which these tubes
and plates were formed, when once it has been subjected to processes of
infiltration by crystallizing mineral and metallic oxides.
Now, I think this argument a very strong one; in fact, although simple,
almost unanswerable. For no _plant_ dwells thus in a house. We have the
plant itself, but nothing more; and if this be not capable, and I hold it
to be incapable, of sustaining the most vehement mineralizing process in
the crucible of Nature, its history must be a brief one, and excepting in
the dark “lithographs” of the coal-measures, its memory must pass away. I
have already allowed an exceptionable case in favour of the _conifers_,
which, be it observed, nowise resemble anything portrayed in siliceous
pebbles, and it is remarkable how much this class of plants predominates
in the COAL.
I have always been suspicious of what are called “vegetable
petrifactions.” I examined those at Tivoli, near Rome, in the year 1845,
and I made up my mind that they are simple _incrustations_. In like
manner, many of the buildings at Pæstum are constructed with a kind
of “travertine” taken from the bed of a neighbouring river, and which
rapidly incrusts any solid objects submitted to the action of its waters.
But the truth is, the vegetable pipe or “straw” remains for a while,
owing to the silex which entered into its composition while the plant
was growing. After some years the _straw_ decays, and there is a hole or
depression in that part of the pillar or pediment. On the other hand, a
calcareous “menstruum,” imbibing silex and iron, hardens into a substance
which, like the best mortar or cement used in building, will sometimes
outlast even the blocks of limestone or oolite which it was put to bind
together.
_Thirdly._ Animal organization, such even as these polyps possessed,
renders the phenomena much more intelligible. Our best authorities in
such matters tell us that “_insects_ have neither lungs nor branchiæ;
but in them the air passes into _a system of tubes_, whose structure
resembles that of an elastic webbing.” And again, “The _annelids_
possess an _uninterrupted circulation_.” And again, “In the ‘Nymphon’
and ‘Pycnogonum’ molluscs, which are crustaceans having considerable
resemblance to certain of our field spiders, the intestine _penetrates to
the very extremities_ of the feet and claws.”—_Animal Kingdom._ Now here
are cited some of the very desiderata which I should have named, had I
been asked what conditions were needed _à priori_ for such petrifactions
to occur. I will only add, under this head, that a fine _annelid_ occurs
in the blue agate off Eastbourne; that a “myriapod,” which is among the
chromo plates of this volume, has all the characteristics of _insect_
life and motion; and that a _spider_ is the nearest thing I know of, in
some respects, to what the “choanite” must have been when that mollusc
condensed himself from a cylinder to a sphere. Perhaps, however, the
strongest clause in this part of the argument may be drawn from the
“sponges.” Here the creature itself, wonderful to relate, is a _viscous
fluid_, and the intricate mansion which he inhabits is a globose,
horny skeleton, perforated with endless small tubes opening into wider
galleries. There was, however, in the perfect animal, I am assured, one
main central cavity, which gave strength and unity to the entire fabric
by the plan of its walls, and, perhaps, by a main valve. Throughout the
whole of this hydraulic system the sea-water, on the circulation of which
the zoophyte depended for life and health, could be pumped to and fro
at pleasure. And, evidently, when the “habitat” of such a creature was
suddenly invaded by a siliceous crystalline solution, extinction of the
animal and a petrifying investment of his abode would be simultaneous.
_Lastly._ If the objects here petrified had been vegetable in their
extraction, should we not, with the aid of the microscope, be able to
identify them? But this I have never yet succeeded in doing; yet all
the petrified “woods” are well known. I have myself obtained slabs of
the “acacia” from the coast of South Devon; of the “beech,” in Sussex;
of coniferous wood almost everywhere. And, what is more to the purpose,
though the petrifaction in such cases is deep and perfect, no one looking
upon it could doubt for a moment that the original structure had been
that of wood from a forest-tree. Agatized as it is, and penetrated here
and there by metallic colours, and shot with rays of jasper, the lines in
its fabric reveal _the texture of wood_.
I may mention here, that every one who walks our beaches, with a view to
the collection of fossil specimens, will do well to carry in his or her
pocket a good lens, of large external diameter; mine measures about two
inches across, and I may truly say it has saved me a world of trouble,
besides affording me much satisfaction at odd moments in the scrutiny of
pebbles of different kinds and textures.
Before closing this chapter I may be permitted to draw the reader’s
attention to a theory held by the late Dr. Mantell. I cannot, at this
moment, lay my hand upon the volume in which it occurs, but I am pretty
sure it will be found in his “Geology of the Isle of Wight:” a book
which, for elegance of composition, and sound information, can hardly
be too much commended; though a resident lapidary in Sandown _did_ once
say to me, while thumbing the pages of a well-worn copy, “Ah, sir!
if the Doctor had come _here_ and stayed a week instead of listening
only to what those fellows told him in Ryde, I could have shown him
something which he doesn’t seem to know, as to how the bit of coast runs
hereabouts.” Dr. Mantell’s idea was this: he held that when a mollusc
was subjected to the first stage in the petrifying process, there was,
in the dying of the creature, some effusion of blood (or _quasi_-blood),
and that this, being the very pith and strength of the animal’s system,
would, in many cases, tinge the future stone indelibly. He carried this
notion so far as to assign some dark blotches, apparent in the masonry of
a wall, to such a source as being their most probable cause; and he gave
to the thing itself the graphic title of _Molluskite_. In this view I
will only add that I am inclined to agree with him; and in my “myriapod,”
already referred to, there is a blood-red spot which pierces through the
stone, appearing on both sides, and which I at first supposed to be a
piece of “shell-lac,” but I now rather regard it as the trace left of
himself by some marauding “pholas,” who, after drilling a hole through
the solid pebble, found his own grave there.