YELLOW SANDSTONE.
Dura Den, whither the scene of our explorations now shifts, occupies a
central position in Fifeshire, and lies equidistant betwixt St. Andrews
and Cupar, the county town. This classic field of geology is therefore
of the easiest access. The railway traverses the opening to the ravine,
a lovely valley of choice archæological as well as fossil remains,
where parliaments have assembled and a scepter was contended for, the
retreat of learned churchmen, and a refuge in the caverns of its rock
for persecuted saints. A day’s excursion to such a place cannot fail to
be a profitable as well as agreeable one, where the students of geology,
or of botany, or of history, will severally meet with objects suitable
to their taste; and, if lovers of the tragic, a short detour to the left
will furnish a sight of Magus Muir, of cruel memory and most indefensible
policy.
The geological structure of Dura Den is more than ordinarily interesting,
presenting, as it does within a limited distance, and in close
juxtaposition, the two series of the old red sandstone and carboniferous
systems, an included mass of overlying trap, a greenstone dyke, and a
vein of galena. The whole length of the dell, with its windings, from the
ruins of the castle resting on the conglomerate red, to the outgoing on
the south into Ceres basin of the coal formation, does not exceed a mile
and a half. The rocks overhang the road which passes through the valley,
the sandstone in some places rising precipitously into bold mural cliffs
of a hundred feet in height, and presenting colored and well-defined
sections of the different layers of which it is composed. These
constitute the fish beds of the yellow sandstone group, lying toward the
northern extremity of the den, and consist of beds of variegated marls,
intermixed with friable arenaceous bands, and hard, compact, fine-grained
building stone.
The carboniferous series are separated from those of the yellow sandstone
by the greenstone dyke referred to, which immediately, and inconveniently
for sight of the junction, interposes betwixt the two systems. The lower
beds of the independent coal formation are here thrown up to an angle of
26°, the yellow sandstone adjacent being nearly horizontal, and in no
place exceeding an inclination of eight or ten degrees. The coal beds
have been lifted up by and repose anticlinally upon the trap, where the
cutting for the road has exposed the outcrop of the seams; and thus,
in a narrow space and lying on the surface, we may mark the outgoing
and the incoming of a vast revolutionary epoch, organic and inorganic,
in the earth’s history. The strata, consisting of alternating bands of
coal, shale, ironstone, and sandstone, assume toward the head of the
valley a nearly horizontal position, abutting against a mass of trap
which separates the lower from the upper workable beds of the bituminous
mineral in the Ceres basin.
Dura Den, in addition to the interest arising from lithological
structure, presents an excellent example of a valley of erosion. The
river which traverses it rises at times into considerable volume,
and sweeps with violence through the pass; connected above, at one
period, with a lake, and acting continuously on soft friable matter,
the abrading powers of the instrument are sufficiently adequate to the
production of the effect. The qualities of the rocks penetrated may be
easily inferred from the windings of the stream—the harder substances
occasioning a divergence from the straight course—the soft and marly
scooped out into wider and more extended areas. A section of any one of
them is thereby labeled for the fullest inspection, which are arranged,
not perpendicularly one upon another, but drawn out in longitudinal
succession on the floor and sidewalls of the valley, and exhibiting to
the geologist, after so many types and forms of the old red sandstone,
the first break and most northern limit of the coal metals in the great
central basin of Scotland.
THE YELLOW SANDSTONE, as it is termed from its prevailing color, though
not uniformly so, belongs to the old red or devonian system of rocks,
of which the cornstone and conglomerate beds are in the immediate
vicinity, and the position and relation of the three to one another
easily determinable. The upper or yellow deposit occupies the valley of
Stratheden nearly throughout its entire length and breadth, and ranges
along the base of the heights of Nydie, Cults, the Lomonds, Binnarty,
and the Cleish hills, dipping under the carboniferous lower group, and
generally separated by overlying masses of trap. The sandstones, indeed,
of both systems, resemble each other so much in color and texture, that
in many instances along the line now indicated the trap must be taken as
a guide by which to ascertain the qualities and respective positions of
the two series. Glenvale, a beautiful ravine which intersects the Lomond
range, presents admirable sections of the whole group, in their regular
order of superposition and finely displaying their contrasting mineral
characters.
ORGANIC REMAINS. These are abundantly distributed in scales, teeth,
spines, coprolites, and other remains, and are to be found in every
opening and quarry throughout the range of the deposit. It is only
in Dura Den, however, that any entire animal forms have as yet been
obtained, and these all confined to a portion of the rock not exceeding
thirty yards by three in breadth, a narrow trough excavated for the
purpose of forming a water-shed to the mill, which stands in the center
of the valley. The fossils derived from this single spot consist of four
new genera, and seven or eight new species, that have been added to
our catalogue of extinct animals. These remains were all in a state of
beautiful preservation; the scales and fins are brightly enameled, and
contrasted with the matrix in which they are set, the colors are as vivid
and glistening as when the animals were sporting in their native element.
The specimens, I believe, of the various collections made in this rich
depository by different parties were all submitted to the examination of
M. Agassiz, who has figured several of them in his “Monograph” on the old
red sandstone, but without completing, it is much to be regretted, his
descriptions of the various fossils. We give the following abridgment of
such descriptions as are contained in the work.
There are two new species of Holoptychius represented, namely,
_Andersoni_ and _Flemingii_, and these are distinguished entirely by
the form and tracery of their respective scales. The H. Andersoni is
described as a small spindle-shaped (_fusiforme_) fish, thick and short,
and narrowing rapidly toward the tail.
[Illustration: Holoptychius Andersoni.]
The scales are much less than those of the other species, as deep as
they are broad, and resembling in general form the scales of the H.
Murchisoni found in Clashbennie. What peculiarly distinguishes them is
the figure of the ornaments (_le dessin des ornemens_) of the surface,
which are parallel, horizontal, very marked and distant in the A. and
never extending in the striæ to the posterior edge. The scales, again, of
H. Flemingii are on the sides of the fish deeper than they are broad, and
on the belly they become rounder. Their ornaments are also very distinct
in the F., consisting of a system of waving lines, which run horizontally
toward the outer edge without any perceptible ramification, while the
wrinkles of the scale rise from a series of little hills (_collines_)
ranged parallel over the length of the inner edge, undulating and very
close. This specimen is represented as very imperfect. The other is
nearly entire, the plates of the head and several of the teeth are well
preserved, every scale is in its place, and the fins are only wanting to
restore the normal outline of the fish. This fossil has been figured and
erroneously described in the author’s “Geology of the County of Fife”
under the name of gyrolepis (holoptychius now) giganteus, from which,
says M. Agassiz, it differs specifically.
From the fossils of this locality has been established the new genus of
GLYPTOPOMUS, the specimen of which being originally mistaken by Agassiz
for a platygnathus, but since found by him to differ from that genus in
several material points. The scales of the platygnathus, for example, are
round and imbricated, possessing in this respect all the characteristics
of the scales of the cœlacanthes, while on the other hand those of the
glyptopomus resemble the scales of the sauroids, which are rhomboidal or
square (_ou carrées_), closely set and never imbricated, as shown in the
subjoined illustration.
[Illustration: Glyptopomus Minor.]
Moreover, the platygnathes are lengthy (_allongés_) in the body, likewise
long (_longue_) in the tail, which is furnished with a very strong
fin, whereas the body of the glyptopomes is very thick, and the tail
short. The ornaments of the scales of G. bear a close affinity to those
generally of the cœlacanthes. Only one species as yet has been found, the
glytopomus minor, and figured in the tab. 26 of the “Monograph” under the
name of platygnathus minor.
The glyptopomus minor, says M. Agassiz, found in Dura Den, and of which
there is but one specimen, is possessed of a body broad and thick,
approaching in form to that of the holoptychius. The fish is lying on
the belly, and turned slightly to the left, so that it is the back and
right side which are represented in the plate. The head is proportionally
small, covered with bones very irregularly carved, presenting a dense
and diversified granular aspect. On the side of the head there is a
large enameled plate, which shows that the cheek was covered, as in the
polypterus, with one single osseous plate, on the under edge of which
was fixed the large masticatory muscle. The scales on the body of the
fish are large, high on the sides, and nearly square on the back, where
in the middle they form an oblique series converging to an acute angle.
The scales are very thick set on the side of each other, and apparently
connected only by means of the skin to which they are attached.
The enameled surface is not smooth, but rather marked with a fine
granulation, which imparts a rich velvet gloss to the scale. Traces only
of the fins are preserved, partly of the ventral, partly of the dorsal
or caudal, and the rays of which are all apparently short and slender.
This specimen forms a part of the author’s collection, but inadvertently
described as belonging to that of Professor Jameson.
Another genus, established from the fossils of Dura Den by M. Agassiz,
is the Pamphractus, of which there are two species, _Hydrophilus_ and
_Andersoni_. These are both in the collection of the author, and have a
special history of their own, from which, when read in all its details,
it would appear they have suffered as roughly at the hands of geologists
in simply determining their class, order, or genus, as they ever did from
the physical revolutions amidst which their lot was originally cast.
Before the type of a new and strange form called _Pterichthys_, had been
determined by this learned palæontologist, collectors were everywhere
puzzled by the specimens of the animal that, from time to time were
casting up. The winged appendages of the sides of the head, as movable
fins, had easily given rise to a variety of opinions concerning their
true affinities, and which, says M. Agassiz, “have been regarded by the
most able naturalists successively as Tortoises, Fishes, Crustacea,
and even Coleoptera.” The fossils of Dura Den were at first regarded
by him as belonging to the type as well as genus Pterichthys, and my
specimens were actually returned from Neufchâtel so named—the “broad”
and “narrow” species—and the label still remains attached. Meanwhile,
five or six species of the genus Pterichthys had been already determined
and described by him, from the fossils of Cromarty and Morayshire—these
in the collection chiefly of Mr. Hugh Miller; and Mr. Miller being,
about the same period, engaged in the preparation of his work, “The
Old Red Sandstone,” speedily under the new nomenclature, as he was so
opportunely furnished with the materials, gave the public the benefit of
M. Agassiz’s discovery and version of their true and authentic history.
What we had hastily, certainly, but still influenced much in the matter
by the judgment of others, referred to the order of Coleoptera, he
was enabled at once, upon the inspection of a Dura Den specimen, and
from its very striking resemblance to his own, to pronounce to be a
Pterichthys. A few pages before he had stated that he could make nothing
of the creature, although some specimens of the fossil had been in his
possession for a period of nearly ten years; but NOW, he was able to
record,—“I very lately enjoyed the pleasure of examining the _bona fide_
ichthyolite itself,—one of the specimens of Dura Den, and apparently one
of the more entire, in the collection of Professor Fleming. Its character
as a Pterichthys I found very obvious.” But short-lived, indeed, are all
mundane enjoyments. The most intellectual, in the revolutions of science,
are not exempt from their general character of vanity. While the two
northern sages were thus gazing, in all the raptures of a new discovery,
“upon the _bona fide_ ichthyolite _itself_,” the philosopher, under the
shelter of the Jura, was doubting, re-examining, and finally correcting,
his own first judgment; and, while the virgin pages of “The Old Red
Sandstone” had scarcely time to reach their author, the “Monograph” was
announcing to the world the determination of a new genus, and that the
fossil of Dura Den was a Pamphractus, and no Pterichthys at all.
“I had at first,” says Agassiz, “connected with pterichthys the only
species known of that genus, by calling it _pterichthys hydrophilus_,
but a more profound study and attentive comparison of that species with
the genus coccosteus, have proved that it ought to form a distinct
genus, intermediate betwixt pterichthys and coccosteus, which I
have named _pamphractus_, in consequence of the divided form of the
carapace. The pectoral fins of pamphractus resemble very much those of
the pterichthys in their form, being slender, elongated, and crooked
(courbée). But the plates of the carapace are all differently arranged.
The central plate is very large (énorme); it covers two-thirds of the
whole carapace, and unites the anterior articulation of the head with
the carapace. The lateral plates, which acquire so great a development
in the pterichthys, are here reduced to narrow stripes, stretching to
the edge of the carapace; while, on the other hand; the posterior plates
are of very great size, and form with a small intercalated plate the
extremity of the carapace. The disposition of the plates of the head is
likewise very different from that of the pterichthys, in which we discern
no thoracic cincture as in that genus, but a transverse line, which
separates in a striking manner the plates of the head from those of the
carapace. _We see not any portion of the tail_; but I presume that it
would bear a resemblance to the form of that of pterichthys.” Agassiz
thus concludes his description of pamphractus, which we have partly
abridged:—“The excessive development of the central plate of the carapace
which reaches the articulation of the head—the absence of a thoracic
cincture making the round of the body—and the distinct separation of the
occipital articulation, will always distinguish this genus from that of
pterichthys.”
Again, however, the ashes of the dead have been disturbed, the history
has been recast, and the old genealogy attempted to be restored. Sir P.
G. Egerton, in a paper read before the Geological Society of London,
on the 19th April, 1848, and a copy of which he did me the honor to
transmit, has examined very minutely every organ and portion of the
animal as delineated in the “Monograph,” and is satisfied that it
is, indeed, still to be regarded as a genuine pterichthys. However,
Sir Philip very cautiously adds,—“Having never seen a specimen of
_pamphractus_, I should not be justified in expressing any positive
opinion respecting this genus, but I cannot help thinking that it is
founded on a specimen, showing the true dorsal arrangement of the
lorication of the Pterichthys.” Accordingly, Mr. Miller, who supplies a
considerable portion of the paper in question, affirms, with abundant
confidence, that he has been able to penetrate the mystery of the error.
“I have succeeded,” he says, “in tracing to its origin the _Pamphractus_
of Agassiz. The specimens which he figures could never have furnished
the materials of his restoration—These materials he evidently derived
from the print of a Pterichthys of the upper Old Red (showing the
dorsal superficies of the creature), given by the Rev. Dr. Anderson of
Newburgh, in his Essay on the Geology of Fifeshire (‘Quarterly Journal
of Agriculture,’ Vol. XI, 1840), as that of a fossil beetle.” Now, with
all submission, this hypothesis is wide of the fact. While Mr. Miller
was inspecting, at Aberdeen, “the bona fide ichthyolite itself,” and
which, as we shall immediately see, was not a Pterichthys, Agassiz had
both the print and the real specimens lying before him. The impressions
on the slab are ELEVEN in number, three of the “broad” and eight of
the “narrow” species; and, comparing the one with the other, the print
with the fossil, he records, “They have been figured VERY FAIRLY by Mr.
Anderson, in his interesting Memoir on the Geology of Fifeshire.” “But,”
adds Mr. Miller, “I have ascertained, by the examination of the greater
number of specimens of this species yet found, in the general outline
of the carapace, which was longer in proportion to its breadth than
in the print, and not defined by such regular curves.” ... The print
is a perfect transcript of the fossil, as if taken in a mold,—curves,
projections, and tubercles all duly and “fairly” preserved, as in the
original; and, with all the materials, and so many actual impressions
before him, Agassiz hesitated not to change his views, and to feel
assured that it was really a Pamphractus, not a Pterichthys, that he
was examining. Farther, we have only to add, that in the Essay in the
Quarterly Journal of Agriculture, it is not true that the print of a
Pterichthys is there “given as that of a fossil beetle;” the higher
patronymic had, ere the publication of the prize essay, been withdrawn;
and the author, along with all others, states, he was waiting the
judgment of the highest and most competent authority from the blue lake
of Neufchâtel.
And thither also, it would now appear, that other inquiries had been
transmitted respecting the organisms of Dura Den, to be famed by modern,
as it had already been by ancient, genealogical claims. We suspect, at
least, it is of “the bona fide ichthyolite itself” that M. Agassiz,
in the “Monograph,” speaks in the following extract:—“Dr. Fleming m’a
communiqué le dessin d’une pétrifaction recueillie par lui à Dura Den,
qui resemble beaucoup, quant à la forme du Pamphractus hydrophilus. La
tête est courte, arrondie, large, presque en forme de croissant, le corps
est allongé, formant avec la tête un ovale qui se termine en pointe en
arrière. Les pectorales sont grêles, courbées et aussi longues que
le corps. L’articulation de la tête avec le corps est très-nettement
marquée, d’une manière qu’a la forme de la carapace près, qui est
beaucoup plus pointue, on croirait voir un Pamphractus. Mais ce qui
distingue surtout ce fossile (à en juger du moins d’après le dessin qui
n’est, à vrai dire, qu’une esquisse) c’est qu’il n’y a pas de plaques
separées, et que toute la surface de sa carapace ne montre qu’une
granulation uniforme et continue, si toutefois la délinéation des plaques
n’a pas été omise par le dessinateur. Nous aurions donc dans ce fossile
un genre nouveau de cephalaspide, caractérisé par la forme de sa tête et
par sa carapace uniforme. Quoi qu’il en soit, j’attends de plus amples
informations sur ce sujet, avant de préciser davantage les caractères de
ce type, et je me borne à reproduire les contours de ce dessin, Tab. 31,
fig. 6, afin de fixer d’une manière plus particulière l’attention sur ce
fossile.”
Now, making every allowance for the imperfection of the sketch of Dr.
Fleming, (qu’une esquisse), and which had not the aggravation of being
a “print,” only see how many marvels have been successively evolved
out of “the _bona fide_ ichthyolite itself:”—it is not a Pamphractus,
though very much resembling it in form—it is not a Pterichthys, of
which alliance there is not a hint even dropped by Agassiz, though its
character as a _Pterichthys_ Mr. Miller “found very obvious;” but “we
have in that fossil a new kind (genre) of cephalaspis, characterized
by the form of its head, and by its uniform carapace,” all which
characters have been overlooked in “the pleasure of examining the
_bona fide_ ichthyolite itself—one of the specimens of Dura Den, and
apparently one of the more entire.” Has this creature undergone a
still further metamorphosis, numerous as those of the Pterichthys
itself? Or what specimen is it which now rejoices in the appellation of
_Homothorax Flemingii_, also again challenged or suspected at least by
Sir P. Egerton, not to be its true designation! But, _quocunque nomine
gaudeat_, the cabinet of science is enriched by the addition of a new and
remarkable fossil fish.
Repeatedly, since the notice in Mr. Miller’s work of the Dura Den fossil,
and his fanciful commentary on the truth and accuracy of the plate in
the “Geology of Fifeshire,” have I examined, compared, and recompared
the design and the original, and never have I been able to detect the
slightest disagreement, even in the minutest feature. Others, and parties
innumerable have examined them freely in my presence, have pronounced as
to the fairness of the representation. There are five figures in all upon
the plate of the Dura Den fossils; they were all, fossils and figures,
under the ocular inspection of M. Agassiz; one of these, _Holoptychius
Andersoni_, he has figured in the “Monograph;” the representations are
identical, and all are declared to be “figured very fairly.” True, the
pamphractus had not been able to preserve the tail, nor any trace even
of that member. Agassiz did not think himself justified in supplying
the deficiency. I added none either, “carefully sinking” the nonentity.
But Mr. Miller had a point to establish: the fossil MUST be one and the
same with the _bona fide_ ichthyolite _itself_, which appears to have
retained the caudal appendage. It will not certainly account for the
obliteration of this organ in ALL the specimens of Dura Den, that, in
common with _Pterichthys_ and _Coccosteus_, the _Pamphractus_ was not
possessed of the _heterocercal_ structure, so characteristic of the
fishes of the period. But yet it is not there. Then, “the tubercles seen
in profile,” are exaggerated: Agassiz thought fit, upon examination, to
retain the exaggeration, as Nature, he perceived, had designed. And now,
Mr. Miller finds it proper to communicate to Sir P. Egerton, that after
examining the specimens (presented by me) in the Museum of the Highland
and Agricultural Society in Edinburgh, “one of the MOST STRIKING specific
distinctions of the creature consists in the length and bulk of the arms,
and the comparatively great prominence of those angular projections by
which they are studded on the edges—projections which seem to be but
exaggerations of those confluent lines of tubercles by which the arms of
all the other species are fringed.” So, Nature has her “exaggerations,”
likewise! and the first of the genus which ever rose to the stroke of the
hammer, has in no degree been misrepresented in its fair proportions,
except that the angular projections referred to are not so prominently
developed as in other specimens in the author’s collection.
It will readily be inferred from all this that the locality of Dura
Den is entitled to much consideration in consequence of the variety
of its interesting remains, not to speak of the diversity of views
which the remains themselves have occasioned in so many quarters. The
Pterichthys, Pamphractus, Homothorax, and Cephalaspis are all of the
family _Lépidöides_, and have such a close affinity in outward form
as readily, in mutilated specimens at least, to be mistaken for each
other. The appendages of the head, having the appearance of wings,
suggested the term _pterichthys_, the winged fish: the plates covering
the body, according to their number and form, gave rise to the generic
distinctions; and the species of each have subsequently been determined
by minor differences. The external organs in all were enameled, and
discover, like the fish of the period, the tuberculated surface. The
Pterichthys of the more northern counties vary in size from nearly a
foot to an inch in length, and generally the wings of these, so far
as they have been figured in works, are extended horizontally and
perpendicularly to the body. The Pamphractus of Dura Den are all nearly
of a size—about two inches and a half in length,—the wings in every
instance depressed and inclined to the sides, and in no instance of the
twenty to thirty specimens exhumed from the rock, has the tail been
appended, or a fragment of the caudal organ detected. The cephalaspis has
only been found in the lower beds of the system, and highly important
would be its discovery in the upper, where, however, we have reason to
think the new genus Homothorax has been substituted in its place. Mrs.
Dalgliesh of Dura, in whose collection we found a Glyptopomus, and a slab
containing several impressions of the Pamphractus, has kindly, and with
a commendable love of science, informed us that her quarries are freely
open for the researches and explorations of geologists, and that every
facility will be afforded them in their interesting task.
In addition to the fossils already referred to, I find in the specimens
of my collection returned from Neufchâtel, that two are labeled as
Diplopterus, new species; two as Glypticus, new species; and one as
Holoptychius, new species. This last is now figured in the “Monograph” as
the Platygnathus Jamesoni. None of these are described in the narrative
of the work, so that until his return from America, where palæontology
will unquestionably reap much from his indomitable perseverance, his
almost instinctive skill, and vast learning, we cannot expect that M.
Agassiz will have leisure either to supplement the deficiencies of his
great work, or confirm his former conclusions against the alterations
suggested in his absence—suggested certainly in no small degree upon
fanciful organization and mistaken assumption.
[Illustration: Platygnathus Jamesoni.]
In closing our review of the old red sandstone, we shall briefly state
the principles of classification of fossil fishes, as determined by M.
Agassiz, from which it will be seen by the earliest types of the marine
vertebrata, while admirably suited to the perturbed condition of the
element in which the strata were formed, differ widely in their structure
from all existing races.
The fishes of the present era, it is well known, are divided into two
great classes, the cartilaginous and the osseous. In the former are
comprehended the sharks, rays, and sturgeons of our present seas; the
latter embrace the salmon, cod, herring, and the various kinds possessed
of similar forms. The bony structure in all the cartilaginous class is
soft, destitute of fibers, and contains scarcely a trace of earthy or
calcareous matter. The osseous fishes, on the other hand, are constructed
internally of true bone, composed of calcareous matter, like that of
birds and quadrupeds, which is possessed of a fibrous arrangement, of
great hardness and capable of long endurance. Now, it would appear that
the fishes of the old red sandstone belong almost exclusively to the
cartilaginous class. The internal frame was composed chiefly of this
soft, soluble substance; hence it is that no portion of the inner
body of the fish, in any of the fossil specimens, remains.—The teeth
and scales, with fragments of the bones of the head, are all that have
survived, but so hard and enduring has been the scaly outer coating, that
the figure and contour of the animal have been preserved entire. The
specimen of Holoptychius Andersoni, from Dura Den, is still enveloped
in its original covering, not a scale in the whole body displaced or
missing, the head and belly slightly compressed, while the posterior
ridge of the back and tail is sharp and angular.
Here, then, in this class of animal life, we find that what is defective
in the internal structure—if it be a defect—is completely supplied in the
outer appendages, whereby the fishes which have the softest bodies are
possessed of hard, horny skins, coated with enamel. Their bones are thus
all on the surface, sometimes in the form of scales; sometimes assuming
the shape of spines and tubercles; now in small, now in large plates;
and often disposed in the most singular and grotesque arrangements, as
in the genus coccosteus, or the osteolepis, whose entire skull consisted
of shining naked bone, and in the cheiracanthus, a creature possessed of
fins scaled and enameled all over.
The Swiss naturalist, accordingly, in adopting a new principle of
classification, so essential in the case of the fossils of the old red
sandstone, has made the scales and external organs the groundwork of his
system. The classification of Cuvier and the older naturalists proceeds
mainly upon the character and disposition of the fins. Hence the order
of the Acanthopterygii, or thorny-finned; and the Malacopterygii, or the
soft finned order.—The classification of M. Agassiz, proceeding upon the
characters of the scales and plates, has given rise to the following
orders, namely, the Placoid, or broad-plated scale; the Ganoid, or the
shining-scale; the Ctenoid, or comb-shaped scale; and the Cycloid, or
marginated scale. Upon the simple basis of these four orders, he has
constructed his system and composed his “Poissons Fossiles,” the standard
authority in fossil ichthyology, and elaborate monument of his learning
and genius.
The relations, as well as distinguishing peculiarities, of the fishes
of the old red, are thus described by Agassiz:—“Of the Placoidian
order,” he says, “the genera ctenacanthus, onchus, ctenoptychius,
and ptychacanthus, are provided with spinous rays to the dorsal fins,
resembling the gigantic ichthyodorulites of the carboniferous and
jurassic formations, but differing in their less considerable size; they
are distinguished among themselves by the forms and ornaments of their
rays. In the order of ganoid fishes, the genera acanthodes, diplacanthus,
cheiracanthus, and cheirolepis present themselves at first sight as a
separate group; for although covered, like the others, with enameled
scales, these are so small, that they impart to the skin the appearance
of shagreen. The manner in which the fins are sustained by spinous rays,
or the absence of these rays, and the position of the fins themselves,
have served as characters in the establishing of these genera. The genera
pterichthys, coccosteus, and cephalaspis, form a second group exceedingly
curious: the considerable development of the head, its size, large plates
which cover it, and which likewise extend over the greater portion of
the trunk, and the movable appendages in the form of a wing, placed on
the side of the head, give to them the most remarkable appearance. It is
these peculiarities, indeed, which caused the class to which these genera
belong for a long time to be misunderstood. The large bony and granulated
plates of coccosteus, led to their being considered as belonging to
trionyx: and it will be sufficient excuse for this error to call to
recollection, that the greatest anatomist of our age had sanctioned this
approximation. The form of the disc of the head of the cephalaspides,
which has the appearance of a large crescent, and their more numerous,
but very elevated scales, resembling the transverse articulations of the
body, explain how it was possible to see in these fishes the trilobites
of a particular genus. Lastly, the winged appendages of the sides of
the head of pterichthys, as movable as fins, have easily given rise to
the variety of opinions concerning the true affinity of these singular
creatures, and has caused them to be taken at one time for gigantic
coleoptera, at another for crustacea, or small marine tortoises; so
little do the types of the classes appear fixed in certain respects
at these remote times. Another singularity of these genera is the
association to the bony plates of the head of a vertebral appendage,
which is far from having acquired the same solidity; but appears, on the
contrary, to have remained fibro-cartilaginous during the whole life of
the animal—resembling in this respect the skeleton of the sturgeon.
“It would be difficult to find among recent fishes, types presenting any
direct analogy with the genera pterichthys, coccosteus, and cephalaspis;
it is only from afar that they can be compared to some abnormal genera
of our epoch.... The analogy which they offer, on the one hand, in form
with the dorsal cord of the embryo of fishes, together with the inferior
position of their mouth, which is equally met with in the embryos; and
on the other hand, the distant resemblance of these fishes to certain
types of reptiles, present the most curious assemblage of characters
that can possibly be conceived. A third group of fishes belonging to
this formation, comprises those genera whose vertical fins are double
on the back and under the tail, and which approach very near to the
caudal. These are the genera dipterus, osteolepis, diplopterus, and
glyptolepis, which differ from one another by the form of their scales
and their dentition. And lastly, it seems necessary to regard as a fourth
group of this order, the genera which are characterized by large conical
teeth, situated on the margin of the jaws, between which are alternately
smaller, and indeed very small ones, in the form of a brush. Such are the
genera holoptychius and platygnathus, and the genus recently established
by Mr. Owen under the name of dendrodus, and respecting which this
learned anatomist has given some exceedingly interesting microscopical
details.”
The philosopher here, in these views as to the primitive diversity of
the ichthyoid types in the old red sandstone, adduces such illustrations
and others not quoted, as subversive of the theory of the successive
transformation of species, and of the descent of organized beings now
living, from a small number of primitive forms. He asserts the doctrine
that the characteristic fossils of each well-marked geological epoch
are the representatives of so many distinct creations, and affirms
that he has demonstrated by a vast number of species that the presumed
identifications are exaggerated approximations of species, resembling one
another, but nevertheless specifically distinct. M. Agassiz introduces
the same doctrine in his latest great work, the “Iconographie,” wherein
he goes the length of saying, that, even when species are, so far as
the eye can judge, identical, they may not be so—that there may exist
species so nearly allied, as to render it impossible to distinguish
them—and reiterates that each geological epoch is characterized by a
distinct system of created beings (the results of a new intervention of
creative power), including not only different species from those of the
preceding system, but also new types. Under his safe guidance we have
glanced at the earliest groups and forms of life upon the globe, and have
seen the simple structures of the beginning succeeded by higher, if not
more perfect or more complex, at least by creatures capable of a wider
range of action and enjoyment. The deductions and sweeping inferences of
geologists may be often vague and uncertain; but a science, whose direct
aim is to decipher the records of the past and compare the successive
types of animal life upon the earth, deals with important objects, and
leads to salutary trains of thought, keeping continually before the view
the Fountain-Head of all being; and adding a new proof to the sublime
doctrine, that Man who is privileged so to range through creation and
time will himself outlive a term of existence, measurable by a few points
of space and a few moments of eternity.
[Illustration: Pamphractus Andersoni.]