The Classifying Principle, and its Uses.--Three groups
of Ichthyolites among the Organisms of the Lower Old
Red Sandstone.--Peculiarities of the Third Group.--Its
Varieties.--Description of the Cheiracanthus.--Of two unnamed
Fossils of the same Order.--Microscopic Beauty of these
Ancient Fish.--Various Styles of Ornament which obtain among
them.--The Molluscs of the Formation.--Remarkable chiefly for
the Union of Modern with Ancient Forms which they exhibit.--Its
Vegetables.--Importance and Interest of the Record which it furnishes.
There rests in the neighborhood of Cromarty, on the upper stratum
of one of the richest ichthyolite beds I have yet seen, a huge
water-rolled boulder of granitic gneiss, which must have been a
traveller, in some of the later periods of geological change, from
a mountain range in the interior highlands of Ross-shire, more
than sixty miles away. It is an uncouth looking mass, several tons
in weight, with a flat upper surface, like that of a table; and
as a table, when engaged in collecting my specimens, I have often
found occasion to employ it. I have covered it over, times without
number, with fragments of fossil fish--with plates, and scales,
and jaws, and fins, and, when the search proved successful, with
entire ichthyolites. Why did I always arrange them, almost without
thinking of the matter, into three groups? Why, even when the mind
was otherwise employed, did the fragments of the _Coccosteus_ and
_Pterichthys_ come to occupy one corner of the stone, and those of
the various fish just described another corner, and the equally
well-marked remains of a yet different division a third corner?
The process seemed almost mechanical, so little did it employ the
attention, and so invariable were the results. The fossils of the
surrounding bed always found their places on the huge stone in
three groups, and at times there was yet a fourth group added--a
group whose organisms belonged not to the animal, but the vegetable
kingdom. What led to the arrangement, or in what did it originate?
In a principle inherent in the human mind--that principle of
classification which we find pervading all science--which gives to
each of the many cells of recollection its appropriate facts--and
without which all knowledge would exist as a disorderly and shapeless
mass, too huge for the memory to grasp, and too heterogeneous for
the understanding to employ. I have described but two of the groups,
and must now say a very little about the principle on which, justly
or otherwise, I used to separate the third, and on the distinctive
differences which rendered the separation so easy.
The recent bony fishes are divided, according to the Cuvierian system
of classification, into two great orders, the soft-finned and the
thorny-finned order--the _Malacopterygii_ and the _Acanthopterygii_.
In the former the rays of the fins are thin, flexible, articulated,
branched: each ray somewhat resembles a jointed bamboo; with this
difference, however, that what seems a single ray at bottom,
branches out into three or four rays a-top. In the latter, (the
thorny-finned order,)--especially in their anterior dorsal, and
perhaps anal fins,--the rays are stiff continuous spikes of bone,
and each stands detached as a spear, without joint or branch. The
perch may be instanced as a familiar illustration of this order--the
gold-fish of the other. Now, between the fins of two sets--shall I
venture to say orders?--of the ichthyolites of the Lower Old Red
Sandstone, an equally striking difference obtains. The fin of the
_Osteolepis_, with its surface of enamelled and minutely jointed
bones, I have already described as a sort of bird-wing fin. The
naked rays, with their flattened surfaces, lay thick together as
feathers in the wing of a bird--so thick as to conceal the connecting
membrane; and fins of similar construction characterized the families
of the _Dipterus_, _Diplopterus_, _Glyptolepis_, _Cheirolepis_,
_Holoptychius_, and, I doubt not, many other families of the same
period, which await the researches of future discoverers. But the
fins of another set of ichthyolites, their contemporaries, may be
described as bat-wing fins: they presented to the water a broad
expanse of membrane; and the solitary ray which survives in each was
not a jointed, but a continuous spear-like ray. The fins of this set,
or order, are thorny-fins, like those of the _Acanthopterygii_; the
anterior edge of each, with the exception of, perhaps, the caudal
fin, which differs in construction from the others, is composed of a
strong, bony spike. Such, with some tacit reference, perhaps, to the
similar Cuvierian principle of classification, were the distinctive
differences, on the strength of which I used to arrange two of my
groups of fossils on the granitic boulder; and the influence of the
same principle, almost instinctively exerted,--for, in writing the
previous pages, I scarce thought of its existence,--has, I find,
given to each group its own chapter.
Of the membranous-finned and thorny-rayed order of ichthyolites,
the _Cheiracanthus_, or thorny-hand, (_i. e._ pectoral,) may be
regarded as an adequate representative. (See Plate VII., fig. 1.)
The _Cheiracanthus_ must have been an eminently handsome little
fish--slim, tapering, and described in all its outlines, whether of
the body or the fins, by gracefully waved lines. It is, however,
a rare matter to find it presenting its original profile in the
stone;--none of the other ichthyolites are so frequently distorted
as the _Cheiracanthus_. It seems to have been more a cartilaginous
and less an osseous fish than most of its contemporaries. However
perfect the specimen, no part of the internal skeleton is ever found,
not even when scales as minute as the point of a pin are preserved,
and every spine stands up in its original place. And hence, perhaps,
a greater degree of flexibility, and consequent distortion. The
body was covered with small angular scales, brightly enamelled, and
delicately fretted into parallel ridges, that run longitudinally
along the upper half of the scale, and leave the posterior portion
of it a smooth, glittering surface. (See Plate VII., fig. 2.) They
diminish in size towards the head, which, from the faint stain left
on the stone, seems to have been composed of cartilage exclusively,
and either covered with skin, or with scales of extreme minuteness.
The lower edge of the operculum bears a tagged fringe, like that of
a curtain. The tail, a fin of considerable power, had the unequal
sided character common to the formation; and the slender and numerous
rays on both sides are separated by so many articulations as to
present the appearance of parallelogramical scales. The other fins
are comparatively of small size. There is a single dorsal placed
about two thirds the entire length of the creature adown the back;
and exactly opposite its posterior edge is the anterior edge of the
anal fin. The ventral fins are placed high upon the belly, somewhat
like those of the perch; the pectorals only a little higher. But
it is rather in the construction of the fins, than their position,
that the peculiarities of the _Cheiracanthus_ are most marked. The
anterior edge of each, as in the pectorals of the existing genera
_Cestracion_ and _Chimæra_, is formed of a strong, large spine. In
the _Chimæra borealis_, a cartilaginous fish of the Northern Ocean,
the spine seems placed in front of the weaker rays, just, if I may
be allowed the comparison, as, in a line of mountaineers engaged in
crossing a swollen torrent, the strongest man in the party is placed
on the upper side of the line, to break off the force of the current
from the rest. In the _Cheiracanthus_, however, each fin seems to
consist of but a single spine, with an angular membrane fixed to
it by one of its sides, and attached to the creature's body on the
other. Its fins are masts and sails--the spine representing the mast,
and the membrane the sail; and it is a curious characteristic of
the order, that the membrane, like the body, of the ichthyolite, is
thickly covered with minute scales. The mouth seems to have opened
a very little under the snout, as in the haddock; and there are no
indications of its having been furnished with teeth.[X]
[Footnote X: There have been three species of _Cheiracanthus_
determined--_C. microlepidotus_, _C. minor_, and _C. Murchisoni_.]
[Illustration: _PLATE VII._]
An ichthyolite first discovered by the writer about three years
ago, and introduced by him to the notice of Agassiz during his
recent visit to Edinburgh, but still unfurnished with a name,[Y]
is a still more striking representative of this order than even
the _Cheiracanthus_. It must have been proportionally thick and
short, like some of the tropical fishes, though rather handsome
than otherwise. (See Plate VIII., fig. 1.) The scales, minute, but
considerably larger than those of the _Cheiracanthus_, are of a
rhomboidal form, and so regularly striated--the striæ converging
to a point at the posterior termination of each scale--that, when
examined with a glass, the body appears as if covered with scallops.
(See Plate VIII., fig. 3.) It seems a piece of exquisite shell-work,
such as we sometimes see on the walls of a grotto. There are two
dorsals--the posterior, immediately over the tail, and directly
opposite the anal fin; the anterior, somewhat higher up than the
ventrals; and all the fins are of great size. The anterior edge of
each is formed of a strong spine, round as the handle of a halbert,
and diminishing gradually and symmetrically to a sharp point. Though
formed externally of solid bone, it seems to have been composed
internally of cartilage, like the bones of some of the osseous
fishes--those of the halibut, for instance; and the place of the
cartilage is generally occupied in the stone by carbonate of lime.
The membrane which formed the body of the fin was covered, like that
of the _Cheiracanthus_, with minute scales, of the same scallop-like
pattern with the rest, but of not more than one sixth the size
of those which cover the creature's sides and back. Imagine two
lug-sails stiffly extended between the deck of a brigantine and her
two masts, the latter raking as far aft as to form an angle of sixty
degrees with the horizon, and some idea may be formed of the dorsals
of this singular fish. They were lug-sails, formed not to be acted
upon by the air, but to act upon the water. None of my specimens show
the head; but, judging from analogies furnished by the other families
of the group, I entertain little doubt that it will be found to be
covered, not by bony plates, but by minute scales, diminishing, as
they approach the snout, into mere points. In none of the specimens
does any part of the internal skeleton survive.
[Footnote Y: Now determined to be a species of _Diplacanthus_--_D.
longispinus_.]
[Illustration: _PLATE VIII._]
My collection contains the remains of yet another fish of this group,
which was unfurnished with a name only a few months ago, but which I
first discovered about five years since. (See Plate VIII., fig. 2.)
It is now designated the _Diplacanthus_; and, though the smallest
ichthyolite of the formation yet known, it is by no means the least
curious. The length from head to tail, in some of my specimens, does
not exceed three inches; the largest fall a little short of five. The
scales, which are of such extreme minuteness that their peculiarities
can be detected by only a powerful glass, resemble those of the
_Cheiracanthus_; but the ridges are more waved, and seem, instead
of running in nearly parallel lines, to converge towards the apex.
There are two dorsals, the one rising immediately from the shoulder,
a little below the nape, the other directly opposite the anal fin.
The ventrals are placed near the middle of the belly. There is a
curious mechanism of shoulder-bone involved with a lateral spine and
with the pectorals. The creature, unlike the _Cheiracanthus_, seems
to have been furnished with jaws of bone: there are fragments of bone
upon the head, tubercled apparently on the outer surface; and minute
cylinders of carbonate of lime running along all the larger bones,
where we find them accidentally laid open, show that they were formed
on internal bases of cartilage. But the best marked characteristic
of the creature is furnished by the spines of its fins, which are
of singular beauty. Each spine resembles a bundle of rods, or,
rather, like a Gothic column, the sculptured semblance of a bundle
of rods, which finely diminish towards a point, sharp and tapering
as that of a rush. (See Plate VIII., fig. 4.)[Z] The rest of the fin
presents the appearance of a mere scaly membrane, and no part of the
internal skeleton appears. Perhaps this last circumstance, common
to all the ichthyolites of the formation, if we except the families
of the _Coccosteus_ and _Pterichthys_, may throw some light on the
apparently membranous condition of fin peculiar to the families
of this order. What appears in the fossil a mere scaly membrane
attached to a single spine of bone, may have had in the living
animal a cartilaginous framework, like the fins of the dog-fish and
thorn-back, that are amply furnished with rays of cartilage--though,
of course, all such rays must have disappeared in the stone, like the
rest of the internal skeleton. Unquestionably, the caudal fin of the
two last described fossils must have been strengthened by some such
internal framework; for, as they differ from the other fins, in being
unprovided with osseous spines, they would have formed, without an
internal skeleton, mere pendulous attachments, altogether unfitted to
serve the purposes of instruments of motion. There may be found in
the bony spines of all this order direct proof that, had there been
an internal skeleton of bone, it would have survived. The spines run
deep into the body, as a ship's masts run deep into her hulk; and we
can see them standing up among the scales to their termination, in
such bold relief, that, from a sort of pictorial illusion, they seem
as if fixed to the creature's sides, and foreshortened, instead of
rising in profile from its back or belly. (See Plate VIII., fig. 1.)
The observer will of course remember, that, in the living animal,
the view of the spine must have terminated with the line of the
profile, just as the view of a vessel's mast terminates with the
deck, though the mast itself penetrates to the interior keel. Now, it
must be deemed equally obvious, that, had the vertebral column been
of bone, not of cartilage, instead of exhibiting no trace, even the
faintest, of having ever existed, it would have stood out in as high
relief as the internal buts or stocks of the spines. And such are the
general characteristics of a few of the ichthyolites of this lower
formation of the Old Red Sandstone--a few of the more striking forms,
sculptured, if I may so speak, on the middle compartment of the
Caithness pyramid. It would be easy rendering the list more complete
at even the present stage, when the field is still so new that almost
every laborer in it can exhibit genera and species unknown to his
brother laborers. The remains of a species of _Holoptychius_ have
been discovered low in the formation, at Orkney, by Dr. Traill;
similar remains have been found in it at Gamrie. In its upper beds
the specimens seem so different from those in the lower, that, in
extensive collections made from the inferior strata of one locality,
Agassiz has been unable to identify a single specimen with the
specimens of collections made from the superior strata of another,
though the genera are the same. Meanwhile there are heads and hands
at work on the subject; Geology has become a Briareus; and I have
little doubt that, in five years hence, this third portion of the Old
Red Sandstone will be found to contain as many distinct varieties
of fossil fish as the whole geological scale was known to contain
fifteen years ago.[AA]
[Footnote Z: Agassiz reckons four species of _Diplacanthus_--_D.
crassispinus_, _D. longispinus_, _D. striatulus_, and _D. striatus_.]
[Footnote AA: This prediction has been already more than
accomplished. At the death of Cuvier, in 1832, there were but
ninety-two species of fossil fish known to the geologist; Agassiz now
enumerates one hundred and five species that belong to the Old Red
Sandstone alone; and if we include doubtful species, on which he has
not authoritatively decided--some of which, however, were included in
the list of Cuvier--one hundred and fifty-one.]
There is something very admirable in the consistency of style which
obtains among the ichthyolites of this formation. In no single fish
of either group do we find two styles of ornament--in scarce any
two fishes do we find exactly the same style. I pass fine buildings
almost every day. In some there is a discordant jumbling--an
Egyptian Sphinx, for instance, placed over a Doric portico; in all
there prevails a vast amount of timid imitation. The one repeats
the other, either in general outline or in the subordinate parts.
But the case is otherwise among the ichthyolites of the Old Red
Sandstone; nor does it lessen the wonder, that their nicer ornaments
should yield their beauty only to the microscope. There is unity of
character in every scale, plate, and fin--unity such as all men of
taste have learned to admire in those three Grecian orders from which
the ingenuity of Rome was content to borrow, when it professed to
invent--in the masculine Doric, the chaste and graceful Ionic, the
exquisitely elegant Corinthian; and yet the unassisted eye fails to
discover the finer evidences of this unity: it would seem as if the
adorable Architect had wrought it out in secret with reference to
the Divine idea alone. The artist who sculptured the cherry-stone
consigned it to a cabinet, and placed a microscope beside it; the
microscopic beauty of these ancient fish was consigned to the
twilight depths of a primeval ocean. There is a feeling which at
times grows upon the painter and the statuary, as if the perception
and love of the beautiful had been sublimed into a kind of moral
sense. Art comes to be pursued for its own sake; the exquisite
conception in the mind, or the elegant and elaborate model, becomes
all in all to the worker, and the dread of criticism or the appetite
of praise almost nothing. And thus, through the influence of a power
somewhat akin to conscience, but whose province is not the just
and the good, but the fair, the refined, the exquisite, have works
prosecuted in solitude, and never intended for the world, been found
fraught with loveliness. Sir Thomas Lawrence, when finishing, with
the most consummate care, a picture intended for a semi-barbarous,
foreign court, was asked why he took so much pains with a piece
destined, perhaps, never to come under the eye of a connoisseur. "I
cannot help it," he replied; "I do the best I can, unable, through a
tyrant feeling, that will not brook offence, to do any thing less."
It would be perhaps over bold to attribute any such overmastering
feeling to the Creator; yet certain it is, that among his creatures
well nigh all approximations towards perfection, in the province in
which it expatiates, owe their origin to it, and that Deity in all
his works is his own rule.
The _Osteolepis_ was cased, I have said, from head to tail, in
complete armor. The head had its plaited mail, the body its scaly
mail, the fins their mail of parallel and jointed bars; the entire
suit glittered with enamel; and every plate, bar, and scale was
dotted with microscopic points. Every ray had its double or treble
punctulated row, every scale or plate its punctulated group; the
markings lie as thickly in proportion to the fields they cover,
as the circular perforations in a lace veil; and the effect,
viewed through the glass, is one of lightness and beauty. In the
_Cheirolepis_ an entirely different style obtains. The enamelled
scales and plates glitter with minute ridges, that show like thorns
in a December morning varnished with ice. Every ray of the fins
presents its serrated edge, every occipital plate and bone its
sculptured prominences, every scale its bunch of prickle-like ridges.
A more rustic style characterized the _Glyptolepis_. The enamel of
the scales and plates is less bright; the sculpturings are executed
on a larger scale, and more rudely finished. The relieved ridges,
waved enough to give them a pendulous appearance, drop adown the
head and body. The rays of the fins, of great length, present also a
pendulous appearance. The bones and scales seem disproportionately
large. There is a general rudeness in the finish of the creature,
if I may so speak, that reminds one of the tattooings of a savage,
or the corresponding style of art in which he ornaments the handle
of his stone-hatchet or his war-club. In the _Cheiracanthus_, on
the contrary, there is much of a minute and cabinet-like elegance.
The silvery smoothness of the fins, dotted with scarcely visible
scales, harmonized with a similar appearance of head; a style of
sculpture resembling the parallel etchings of the line-engraver
fretted the scales; the fins were small, and the contour elegant. I
have already described the appearance of the unnamed fossils--the
seeming shell-work that covered the sides of the one--its mast-like
spines and sail-like fins; and the Gothic-like peculiarities that
characterized the other--its rodded, obelisk-like spines, and the
external framework of bone that stretched along its pectorals.
Till very lately, it was held that the Old Red Sandstone of Scotland
contained no mollusca. It seemed difficult, however, to imagine a sea
abounding in fish, and yet devoid of shells. In all my explorations,
therefore, I had an eye to the discovery of the latter, and on two
several occasions I disinterred what I supposed might have formed
portions of a cardium or terebratula. On applying the glass, however,
the punctulated character of the surface showed that the supposed
shells were but parts of the concave helmet-like plate that covered
the snout of the _Osteolepis_. In the ichthyolite beds of Cromarty
and Ross, of Moray, Banff, Perth, Forfar, Fife, and Berwickshire, not
a single shell has yet been found; but there have been discovered of
late, in the upper beds of the Lower Old Red Sandstone in Orkney,
the remains of a small, delicate bivalve, not yet described or
figured, but which very much resembles a _Venus_. (See Plate V.,
fig. 7.) In the Tilestones of England, so carefully described by
Mr. Murchison in his _Silurian System_, shells are very abundant;
and the fact may now be regarded as established, that the Tilestones
of England belong to a deposit contemporaneous with the ichthyolite
beds of Caithness and Cromarty. They occupy the same place low in
the base of the Old Red; and there is at least one ichthyolite
common to both,[AB] and which does not occur in the superior strata
of the system in either country--the _Dipterus macrolepidotus_. The
evidence that the fish and shells lived in the same period, and
represent, therefore, the same formation, may be summed up in a
single sentence. We learn from the Geology of Caithness that this
species of _Dipterus_ was unquestionably contemporary with all
the other ichthyolites described;--we learn from the Geology of
Herefordshire that the shells were as unquestionably contemporary
with it.[AC] These--the shells--are of a singularly mixed character,
regarded as a group, uniting, says Mr. Murchison, forms at one time
deemed characteristic of the more modern formations,--of the latter
secondary, and even tertiary periods,--with forms the most ancient,
and which characterize the molluscous remains of the transition
rocks. Turbinated shells and bivalves of well nigh the recent type
may be found lying side by side with chambered Orthoceratites and
Terebratula.[AD]
[Footnote AB: _Silurian System_, part ii. p. 599.]
[Footnote AC: In Russia, too, as shown by the recent discoveries of
Murchison, the Old Red fishes of Caithness, and the Old Red shells of
Devonshire, may be found lying embedded in the same strata.]
[Footnote AD: _Silurian System_, part i. p. 183.]
The vegetable remains of the formation are numerous, but obscure,
consisting mostly of carbonaceous markings, such as might be formed
by comminuted sea-weed. (See Plate VII.) Some of the impressions
fork into branches at acute angles, (see figs. 4, 5, and 6;) some
affect a waved outline, (see figs. 7 and 8;) most of them, however,
are straight and undivided. They lie in some places so thickly in
layers as to give the stone in which they occur a slaty character.
One of my specimens shows minute markings, somewhat resembling the
bird-like eyes of the Stigmaria Ficoides of the Coal Measures;--the
branches of another terminate in minute hooks, that remind one of the
hooks of the young tendrils of the pea when they first begin to turn.
(See fig. 3.) In yet another there are marks of the ligneous fibre;
when examined by the glass, it resembles a bundle of horse-hairs
lying stretched in parallel lines; and in this specimen alone have
I found aught approaching to proof of a terrestrial origin. The
deposition seems to have taken place far from land; and this lignite,
if in reality such, had probably drifted far ere it at length became
weightier than the supporting fluid, and sank.[AE] It is by no means
rare to find fragments of wood that have been borne out to sea by the
gulf stream from the shores of Mexico or the West Indian Islands,
stranded on the rocky coasts of Orkney and Shetland.
[Footnote AE: The organism here referred to has been since slit by
the lapidary, and the sections carefully examined. It proves to be
unequivocally a true wood of the coniferous class. The following
is the decision regarding it of Mr. William Nicol, of Edinburgh,
confessedly one of our highest living authorities in that division
of fossil botany which takes cognizance of the internal structure cf
lignites, and decides from their anatomy their race and family:--
Edinburgh, 19th July, 1815.
Dear Sir:--I have examined the structure of the fossil wood
which you found in the Old Red Sandstone at Cromarty, and have
no hesitation in stating, that the reticulated texture of the
transverse sections, though somewhat compressed, clearly indicates
a coniferous origin; but as there is not the slightest trace of
a disk to be seen in the longitudinal sections parallel to the
medullary rays, it is impossible to say whether it belongs to the
Pine or Araucarian division. I am, &c.,
William Nicol.
]
The dissimilarity which obtains between the fossils of the
contemporary formations of this system in England and Scotland, is
instructive. The group in the one consists mainly of molluscous
animals; in the other, almost entirely of ichthyolites, and what
seems to have been algæ. Other localities may present us with yet
different groups of the same period--with the productions of its
coasts, its lakes, and its rivers. At present, we are but beginning
to know just a little of its littoral shells, and of the fish of its
profounder depths. These last are surely curious subjects of inquiry.
We cannot catechise our stony ichthyolites, as the necromantic lady
of the _Arabian Nights_ did the colored fish of the lake, which had
once been a city, when she touched their dead bodies with her wand,
and they straightway raised their heads and replied to her queries.
We would have many a question to ask them if we could--questions
never to be solved. But even the contemplation of their remains is
a powerful stimulant to thought. The wonders of Geology exercise
every faculty of the mind--reason; memory, imagination; and though
we cannot put our fossils to the question, it is something to be
so aroused as to be made to put questions to one's self. I have
referred to the consistency of style which obtained among these
ancient fishes--the unity of character which marked every scale,
plate, and fin of every various family, and which distinguished it
from the rest; and who can doubt that the same shades of variety
existed in their habits and their instincts? We speak of the infinity
of Deity--of his inexhaustible variety of mind; but we speak of it
until the idea becomes a piece of mere common-place in our mouths. It
is well to be brought to feel, if not to conceive of it--to be made
to know that we ourselves are barren-minded, and that in Him "all
fulness dwelleth." Succeeding creations, each with its myriads of
existences, do not exhaust Him. He never repeats Himself. The curtain
drops, at his command, over one scene of existence full of wisdom
and beauty; it rises again, and all is glorious, wise, and beautiful
as before, and all is new, Who can sum up the amount of wisdom
whose record He has written in the rocks--wisdom exhibited in the
succeeding creations of earth, ere man was, but which was exhibited
surely not in vain? May we not say with Milton,--
Think not, though men were none,
That heaven could want spectators, God want praise;
Millions of spiritual creatures walked the earth,
And these with ceaseless praise his works beheld?
It is well to return on the record, and to read in its unequivocal
characters the lessons which it was intended to teach. Infidelity has
often misinterpreted its meaning, but not the less on that account
has it been inscribed for purposes alike wise and benevolent. Is
it nothing to be taught, with a demonstrative evidence which the
metaphysician cannot supply, that races are not eternal--that every
family had its beginning, and that whole creations have come to an
end?