THE DEVONIAN SYSTEM, OR OLD RED SANDSTONE.
A geologist requires not, like the tourist, to be told of the various
conflicting roads that run among the mountains, in what precise course
he is to wend his way. He will follow his own pathways, roads of
nature’s forming, guided by the strike and lie of the rocks rather
than by the beaten tracks of every-day life. But come whither he
will—through Glentilt, Glenericht, Glenbeg, and the Spittal, Glenisla,
and Clova,—or along the Dee, the heights of Glentanner, and penetrating
to the sources of the Esks—sure we are, when he reaches by any of those
passes the frontiers of the Grampians, he will pause and gaze wistfully,
thoughtfully, admiringly, ere he descends, upon the magnificent prospect
that stretches before him, unrivaled by any on the terraqueous globe. The
GRAN-PEN, _celticé_, the shelvy or precipitous summit, Romanized into
Grampius, has its own inner charms, peaceful rock-girt valleys where
princes dwell, and happy as Rasselas ever trod.—And escaped from these,
what an outer world beneath, fertile, abundant, replete with everything
that can charm the eye or interest the student. Looming in the far
distance, the Lammermuirs, of silurian origin, can just be descried as
a dark-blue line on the verge of the horizon; the Ochils and Lomonds,
of carboniferous age, repose like islets on the pendant sky; while, in
the foreground of the picture, there is the most charming variety of
woodland, meadow, farmstead, town, and mansion, all as I now gaze upon
them in their autumn coloring, invested with a Claud-like mellowness that
speaks with a moral yet romantic sympathy to the heart. The round tower
of Brechin, the moldering walls of Edzell, the frowning battlements of
Glammis, the worn-out and now verdant ramparts of Dunsinane, have each
their crowds of visitants, and are all within the compass of a single
day’s journey.
The eye of the geologist is in search of another object as it wanders
over that lovely scene: Kinnordie, the birth-place of Sir Charles
Lyell, must ever be classic ground in the history of our science. It
rests on the old red sandstone, and furnishes some of the most valuable
illustrations in Sir Charles’s early sketches. What influences, may
we here ask, gave being and shape to the ingenious and splendid
generalizations of this accomplished geologist? Is it too much to assume
that the philosopher, as well as the poet, is all his life-long captive
to first impressions, that the scenes of his boyhood claim “a local
habitation” for many of his future speculations, and that his most
matured trains of thinking have been dependent upon casual circumstances?
Born and educated in the shadow of the Grampians, who can doubt that the
spirit within was early stirred to lofty views as he gazed upon their
elevated forms, and wondered how their peaks rose so high in air, and
were thus lifted above the valleys? May it not be presumed, though the
philosopher himself may have no recollection of the matter, that his
speculations regarding the alternate elevation and depression of land and
sea had its germ in some such happy moment of mountain inspiration? Byron
owned the influence in all its power, when, in the rocky defiles and dark
pine forests of Lochnagar, he had early communings with spiritual beings,
the wreathe-forms and kelpies of the streams; and in visions imparted
amidst the wilds of the Dee, prepared his mind for the daring flights
of the Alps. The geologist had here all the materials of after-thought,
which in his various essays and works he has so skillfully expanded—from
his explorations of Bakie-loch with its alluvions, peat, marl, shells,
and horns, in which he had the type of some of his Alpine tertiaries—the
old canoe and ripple-mark here too, the representatives of their
far-sundered ages and onward to his bold speculations on the elevatory
hypothesis, of which the Grampians, as well as Sidlaws, supplied him with
ample illustrations.
The descent from the mountains upon the series of rocks that occupy the
plains, is one not merely of space, but likewise of time. A geological
epoch has vanished, and a new order of things has been called into
existence. This implies a change in the animal as well as in the mineral
kingdom. The change may not have been sudden, but it has been thorough
and pervading, accompanied by circumstances that show a general shift
in the sea-bottom, and causes that have been nearly uniform in their
operation over the surface of the globe. The shift in the sea-bottom is
detected in the elevation of the silurian group of rocks, which have
been lifted from a horizontal into a highly-inclined position: in some
instances they are nearly vertical; and in most cases where the igneous
rocks occur, they are bent and twisted, greatly altered and disrupted, by
the process of upheaval to which they have been subjected.
Geology notes in this an epoch or age of organic existence. The
superjacent series of rocks are seen lying unconformably upon the
silurians, that is, the older series had been consolidated and upheaved,
and a period of intervening time had elapsed before the deposition of the
newer. The fossils imbedded are likewise distinct and peculiar—one and
the same over the superficial area of the globe—and thus we learn to mark
the great and interesting cosmical changes which had already begun to be
effected. We are now among the Old Red Sandstone, or Devonian system of
rocks, so denominated from their great development in that district of
the sister kingdom.
As contrasted with the former system, the rocks of this period indicate
considerable disturbance in the waters of the ocean, currents and
agitations widely prevailing, and perhaps also deeper seas. The crust
of the earth was still rising, and the mountains becoming higher, and
these effects would necessarily follow. A superior order of animals
were introduced. The fishes, which begin to appear in the upper beds of
the silurian group, are now increased both in numbers and in variety of
structures. The invertebrata were the prevailing types of the former
age. The old red sandstone is pre-eminently characterized by the
vertebrata, when, completely adapted to the element to be inhabited,
mailed and plated over with thick horny scales, huge bony heads, fins
and tails of corresponding strength and size; the Sauroid family appear
upon the stage, capable all of buffeting the waves and fulfilling their
destiny amid the greatest commotions. The fish of this early period are
generally well preserved, even better than those of the tertiary age,
in consequence of their osseous scales being harder than the bones, and
which, from their interlocked arrangement, have contributed to preserve
the general form of the body when the inner skeleton has disappeared and
every other part and organ have been destroyed.
The old red sandstone formation is very extensively distributed in
the northern counties, forming a great belt round the coast from
Caithness-shire to Aberdeenshire, and consisting of three well-marked
divisions, the lower, middle, and upper series of beds. The strata flank
the northern walls of the Grampians and their out-liers, traversing the
great central or Caledonian valley for a hundred miles, and training
round the western coast by Oban, the shores of Mull and Morven. They
are of great thickness in many places; and in some of the beds, as at
Cromarty, Lethen-bar, and Gamrie, contain nearly all the fossils peculiar
to the formation.
The order of Ganoid fishes, which afterward fulfill so distinguished
a part in the kingdom of nature, is wholly absent from the silurian
group, while, in the Devonian, nearly thirty genera, and considerably
above sixty species, have been described and named. The scales of
these creatures would appear to have been richly ornamented, enameled,
and shining, and hence the term Ganoid applied to the order. In the
northern districts, beyond Ben Mac-Dhui, the following genera, with
several species belonging to each, have been found, namely, coccosteus,
cheiracanthus, cheirolepis, dipterus, diplopterus, diplocanthus,
glyptolepis, osteolepis, pterichthys. The principal localities of these
fossils are—the Dipple on the Spey, Tynet Burn in Banffshire, Seat-Craig
near Elgin, Altyre on the Findhorn, Clune, and Lethen-bar in Nairnshire,
Gamrie, Cromarty, and various places in Sutherland and Caithness.
Shetland is chiefly composed of the old red sandstone, which yields
abundantly the fossils peculiar to the deposit. The formation extends
through the Orkney islands, inexhaustibly fertile in organic remains,
and among which have been found plates and fragments of the Asterolepis,
the largest of all the genera belonging to the period: the head and
jaws, at least, appear to have been of enormous dimensions, and portions
of the inner skeleton must have been bony, contrary to the general
cartilaginous structure of the class. The Placoids of the subjacent
rocks have many resemblances to the cestracions, centrinæ, and spinaxes
of our present seas, their scales being set like plates at irregular
distances over the body. The Ganoids, on the other hand, whose scales
were continuous, and enveloped the entire animal, have no affinities to
any living types.
Specimens of vegetable organisms are very common in some of the
flagstones of Orkney, resembling, in some instances, the Lycopodiaceæ,
or club-mosses, so abundant in the carboniferous strata: and branching
fucoid plants, of which portions have been found from two to three feet
in length, and of nearly the same diameter of stem throughout. But in
tracing the COURSE of CREATION in this department of her works, the most
important fact to relate is, the discovery of a coniferous lignite,
imbedded in the old red sandstone of Cromarty. This interesting relic
was obtained from these beds, several years ago, by Mr. Miller; and,
though still of that remote age an instantia solitaria of its kind, like
the foot-print of Robinson Crusoe, it is the sure token of a race that
inhabited the island, and harbinger of a luxuriant flora then waving
along the shores of the boundless waters. These northern localities, on
the mainland, as well as in the islands, are also remarkable for their
shell-beds in this deposit, while very few of such organisms have yet
been detected in any of the Scottish rocks of the system to the south
of the Grampians. The relics are confined to one species of shell,
resembling in general appearance the form of the Cyclas, and are found in
various quarries in the district.
What a revolution in letters, knowledge, and civilization since the days
of the Romans! This, their Ultima Thule! and a science in the very rocks
of which they never even dreamed. Proud they were of their fabled origin
from the twin boys suckled by the wolves. Here are the spoils of ages
long anterior to their myths of remotest genealogy—families of creatures
that had fulfilled their destiny—buried in the sand, and upheaved into
lofty mountains, while the Seven Hills of their proud city slept beneath
the waves.
We now proceed to trace the order of the formation southward of the
Grampian chain.
1. The conglomerate, a deep red and well-marked deposit, skirts the
base of the mountains, and in some places is of vast thickness, betwixt
Stonehaven and Blairgowrie. This rock is composed of fragments of
the primary series, gneiss, mica-slate, quartz, and porphyry; the
granite constitutes the paste in which these are set and agglutinated
together. Excellent sections are to be seen in those localities,
where the principal rivers, the North and South Esks, the Wast Water,
the Isla, and the Ericht, make their passage in debouching upon the
plains. In all these defiles the cliffs are precipitous, and often very
picturesque, their variegated and bright flesh-colored sides forming
a pleasing contrast with the dark waters as they eddy into pools, or
dash headlong over their broken ledges. A momentary inspection of this
composite rock leaves not the shadow of a doubt upon the mind as to
its derivative origin, while its vicinity to the great chain where its
several ingredients are to be found as directly points to the quarry
whence it was hewn: not, it may be, slowly accumulating, as generally
asserted, during the lapse of indefinite periods of time, but rapidly
brought together and consolidated, as so many of the sharp angular
edges of the materials most unequivocally attest. The finer beds that
occur in the vicinity would seem to have been the talus or outgoing
of the coarser conglomerate, formed of the minute particles of the
same ingredients which had accumulated in the more tranquil hollows of
the sea-bottom. The slaty fissile sandstone of Coventry Quarry near
Fettercairn (so remarkably tilted up and welded literally to the igneous
dyke), stretching throughout the north-east and south-west parts of the
counties of Kincardine and Forfar, and prevailing over the districts of
Auchtergaven, Crieff, and Callander, may be mistaken in many places for
the clay-slate itself slightly altered in texture and appearance.
These conclusions as to the derivative origin of the conglomerate are
fully confirmed and borne out by the fact, that the deposit is everywhere
found precisely where such materials would be collected, all around the
shores of the Scottish Highlands, overlying or fringing the base of
the crystalline rocks, filling up the creeks and bays of the primeval
world. After thousands of years the massive blocks of syenite, chiseled
and half-dressed, are still lying in the quarries of Upper Syria,
while the cities for which they were preparing are heaps of ruins in
the desert. Nature, left to her own operations, treasures up the waste
occasioned by the elements and other forces, and by thus raising outworks
and buttresses protects her crystal foundations against the inroads of
consuming time.
2. Forming an outer zone or rampart, and overlapping the conglomerate, a
gray fossiliferous sandstone constitutes the next member of the Devonian
group. This deposit is widely extended, and consists of several beds.
One of these is a fine-grained, compact building stone. Another, the
well-known flag-stone, is of a more slaty texture, of a dark-blue color,
and abounds in mica. These sandstones occupy a great part of the sea-ward
barrier by Montrose, Arbroath, and the high grounds of Carmylie. They
fold over the Sidlaws on both acclivities of the range, where they form
a well defined example of what geologists term the _anticlinal_ and
_synclinal_ axes, that is, the rock curves and reduplicates, like a soft
flexible substance, according to the undulations of the surface. The
several beds cross the Tay in the direction of Dundee, and emerge on the
opposite banks at Wormit-bay, Parkhill, and Newburgh; ranging eastward
along the northern slope of the Ochils by Norman’s Law and the high
table-land of Balmerino.
3. A limestone rock, termed CORNSTONE, from its practical application
to grinding purposes in England, occupies a place among the old red
sandstone series. This deposit occurs in thin bands of a dull yellowish
or blue-colored stone, containing numerous cherty nodules, and, where
compact, is of a sub-crystalline texture. The cornstone generally
contains more of silicious than of calcareous matter, and is consequently
not much prized for building or agricultural purposes. In Scotland no
organisms have been as yet detected in it, but in England it yields
abundantly remains of the cephalaspis and various crustaceans. This
rock is not co-extensive with the other members of the group, nor do we
find it continuous in any part of the district which it occupies. It is
generally found in small detached patches, as at Glen-Finlay, Meigle,
Cargill, on the north of the Sidlaws; at Ballendean, Rait, Meurie, in the
Carse of Gowrie; at Parkhill, Newburgh, Clunie, Kinnaird, on the south
bank of the Tay; and at Newton and Craigfoodie, on the southern face of
the Ochils. At the Newburgh station of the Edinburgh and Northern Railway
the cornstone is inclosed among the eruptive rocks, partaking of their
common induration, and, except in its distinct lamination, cannot be
distinguished in color or texture from the traps.
4. A rock-marl underlies the cornstone in the form of a reddish,
variegated sandstone, and contains about fifteen per cent. of lime.
Deep sections of this calcareo-arenaceous deposit are displayed along
the basin of the Tay, on both sides, from the confluence of the Isla
to Stanley, at Pitcairn Green on the Almond, and occupy the ridge from
Methven to Crieff. A remarkable vein of serpentine skirts the base of the
Grampians in a south-east and north-west direction, of a beautiful dark
olive-green, in some places of a blue and whitish color, and at Cortachie
Bridge, where it crosses the Esk, containing crystals of diallage. This
dyke widens in some parts to nearly ninety feet, of a hard compact
texture, and, as the marble of the district on the lakes of Clunie, it is
extensively used for ornamental purposes.
5. The geologist, as he pursues his journey by either of the lines of
railway that intersect Forfarshire, has still many interesting localities
and objects before him. Traversing “the fertile plains of Gowrie” by the
Perth and Dundee Junction, he enters at Inchture upon a higher member of
the old red sandstone, a fine-grained yellow-spotted bed. The deposit
first appears to the eastward of Inchture, in the den of Balruddery,
where its outcrop is seen immediately to overlie the gray fossiliferous
beds.—The same variety emerges on the opposite bank of the Tay at
Birkhill; at Abernethy, where it abuts at nearly right angles against the
trap in a small ravine to the south of the village; whence it skirts the
base of the Ochils, and occupies the center of Strathearn at Dumbarnie.
The Clash-bennie sandstone, doubly interesting from having furnished the
first and best specimen of holoptychius, the type of its age, may be
regarded as an extension of the Balruddery and Inchture rock. The beds
vary a little in their lithological characters, as well as in the deep
flesh-color predominant in the latter; still the spherical markings are
there, and, as their organic remains are identical, their position in the
series may be considered as one and the same. The yellow or upper beds of
the old red sandstone fall next to be considered; but these, from their
geographical limits, are deferred to the subsequent chapter.
6. Approaching Perth by the Midland Junction, the geologist cannot fail
to be arrested by the vast accumulations of sand and gravel, which
everywhere present themselves, sometimes in the deep cuttings and
railway sections; sometimes in the shape of rounded hillocks or long
narrow ridges; and at other places as extended plateaux or sea-margins
of different elevations. Along the whole western and southern slopes
that overhang the city, these objects give a pleasing variety to the
landscape, and form interesting subjects of speculation as to their
origin, doubtless the gathered wreck of all the rocks we have been
contemplating; for after a careful examination of their contents the
conclusion cannot be avoided, that with much of the spoil of the primary
rocks, we have here the detrital waste of the entire old red sandstone
series. The Carpow cutting, in Strathearn near Newburgh, contains large
rounded masses of all the varieties, with their peculiar ichthyolites;
the gray, red, and yellow deposit that prevails in Fifeshire, and one
solitary patch of which still exists _in situ_, near the Kirk of Dron, as
if on purpose to mark its ancient and more extended boundaries. Nodules
and bowlders of the cornstone are likewise abundant. In the vicinity
of Perth, the waste of the yellow sandstone is to be found, unmixed in
several spots, consisting of thick beds of fine argillaceous sand.
Similar masses of gravelly debris are spread over the middle-basin
of the Earn, from Forteviot to Muthil. The Scottish Central cleaves
its way for ten miles through scarcely any other material. The dreary
monotony of these endless hillocks, around Auchterarder and Blackford,
is relieved in part by the fine undulating grassy braes of the Ochils,
and the richly-wooded rising grounds skirting the left bank of the river.
The geologist’s eye wanders eastward, through the district occupied by
the lower basin of the Tay, where the whole was one great estuary or
strait, and these the shoals covered by the ancient waters. The eastern
shores, from Wormit-bay to Leuchars, are accordingly characterized by
vast accumulations of sand and gravel, originating in the same causes and
deposited at the same period.
It will excite no surprise, therefore, should we remark that the various
beds of old red sandstone now so disjoined, or appearing only as patches,
once covered the greater part of the district traced above, extending
from the Ochils across the Sidlaws to the Grampians. Nor can there be
difficulty in finding an adequate cause for their up-break, especially
in the upper members of the group. Consider not merely the constant
waste arising from aqueous abrasion and meteroic influences, but also
the tearing effects occasioned by the convulsive throes and elevatory
movements of the Grampian, Sidlaw, and Ochil ranges, either singly, or,
as it may have happened, in combination, when the overlying rocks must
have been shattered and broken in every direction, and rendered capable
of easy transportation. Although belonging to a posterior geological
epoch, these hillocks of gravel and sand are thus the collected records
of primeval times, attesting that mighty agencies have been at work in
rending the globe, re-adjusting its materials, and preparing them for
future combinations.
How speedily, in these first days of creation, does geology make us
acquainted with the liability to change and mutation stamped upon
all earthly things! The mountains are raised up, and their earliest
struggles are to get down again. Nor is it the law of matter, if we may
use the expression, to rise. The waters seek the hollows of the earth,
because they are material. The rocks, more solid, are subject to the
same principle of gravitation, and their course is downward, and their
natural place the bottom of the waters. When the rocks were separated
from and elevated above the waters, it was not by any virtue or power
in themselves to assume these positions. The separation as well as the
elevation were the results of direct arrangement; both certainly provided
for in the original plan, and yet not the less brought about against
their own material tendencies by a special agency. Geology thereby
establishes the fact, that the mountains were raised up and the dry land
COMMANDED to appear. And now, decomposing and wasting down, we see them
seeking back to their old places, to be there re-constructed, and to
subserve other purposes.
THE ORGANIC REMAINS, which fall next to be described, are confined to
three of the beds, as enumerated above. The first of these, in the order
of superposition, is the micaceous flagstone of Carmylie and Arbroath,
likewise extending along the south bank of the Tay, and distinguished
by the vegetable culmiferous impressions with which it abounds. These,
in some places, are so numerous, as to cover the entire surface of the
rock. The idea of an ancient marsh is immediately called up in the mind,
as one sees stone after stone split up, and all the interstices mottled
and streaked over with the stems and leaves of the plants which were
fed by its waters. While we write, every pond, and every lake in the
neighborhood has crept quietly under its carpeting of ice, a congelation
of the living with the dead. How beautiful and distinctly delineated the
culms and leaves of the chara locked in its crystal embrace; the flower
of the juncus yet lingers on the stalk; and there, how gracefully float
the long broad continuous stems of the scirpus lacustris! The pike and
perch, both typified in the olden rocks, may be seen motionless as a
stone, or softly buoyant as the down, in the clear depths below. Not so
brightly, but now as fixedly set, and as minutely preserved, are the
fragments of the flora of the Devonian age: if blackened and jetty in
their hoary antiquity, these films of mica give light and relief to the
darker background of the picture; and shapes, too, were there sporting in
the waters,—the seraphim and buckler-headed cephalaspis,—which painter
never conceived, nor poet feigned.
These fossils are not in a state of petrifaction, but generally consist
in the form of an easily-separated film of carbonaceous matter, or more
frequently as a simple coaly marking. Sometimes, but very rarely, the
plant is found betwixt the slaty layers, as it were in a dried state, and
still perfectly flexible; and the impressions not unfrequently resemble
the narrow striated leaves of the alopecurus geniculatus, the floating
foxtail-grass, with its knotted culms. There are other specimens, that
look like the bark of trees, or the branches of the gnarled oak, ribbed
and jointed crosswise. The round dotted patches, varying from the size of
a garden pea to an inch in diameter, not unlike, in shape and appearance,
the form of a compressed strawberry, are very plentiful. Dr. Fleming,
in Cheek’s “Edinburgh Journal” for February, 1831, has figured this
organism in connection with the stem, which thereby forms a graceful and
well-defined flowering plant, while Sir Charles Lyell considers these
berry-shaped forms to be the relics of the ova of some gasteropoda of the
period. But at Wormit and Parkhill they are so uniformly, and in such
numbers, associated with the culmiferous and leaf impressions, as most
strongly to vindicate their claim to a vegetable origin. We have in our
collection several specimens, with this organism separated certainly from
the culm, but still in such closeness and proportionate size, as, with
little aid from the imagination, to infer their former connection, and
assign to them a place among the phanerogamous and seed-yielding plants.
If so, we cannot too highly prize these relics, regarding them, as they
undoubtedly are, among the oldest of organic substances—the first of the
green herbs that sprung from the earth—the fragile flower, that withers
often in a day, there to attest the mandate of primeval creation. How
many seasons have returned; how many seed-times and harvests have covered
the fields; what revolutions and changes over all these hills and plains,
since that flinty rock formed the soil, and these vegetables sprung from
its fertility! They are not admitted among the economic order of the
gramineæ; nor whether of marine, semi-marine, or lacustrine origin, have
geologists been able to determine.
Of the ANIMAL REMAINS of fishes belonging to the gray sandstone, the
Cephalaspis Lyellii was one of the earliest discovered, as it still
constitutes one of the most remarkable of these fossil relics. The
head of this creature, and hence the name buckler-headed, is large in
proportion to the body, forming nearly one-third of its length. The
outline is rounded in the form of a crescent, the lateral horns inclining
slightly toward each other, while the anterior or central parts project
considerably outward; this peculiarity of structure is occasioned by the
intimate anchylosis of all the plates which compose the cranium. The
body resembles in appearance an elongated spindle, swelling out on the
ridge of the back, and narrowing to the extremity of the tail, which
terminates in a long slender point. How like, peradventure, the very
dagger with which the murderous Thane of Glammis threatened to render—
“The multitudinous seas incarnadine,
Making the green one red!”
The sanguineous fluid, in those days, was not indeed very plentiful;
but the sharp-horned orthoceræ, and the swift predaceous nautili were
cotemporaries; and hence, either for protection or attack, we find that,
while the head of the Cephalaspis was one entire plate of enameled
bone in the upper division, the body was wrapped in a closely woven
net-work of bony scales, of peculiar form, and differing from the scales
of every other genus of ganoids. The scales along the center of the
sides are so high, that their breadth exceeds their length eight or ten
times, occupying more than half the height of the animal. Everywhere
meshed in smaller but equally impervious nettings, there are of the
larger scales, from twenty-six to thirty covering the sides, thereby
completing a mail-clad figure of a singularly warlike aspect, and bidding
defiance, like his great anti-type, to all his foes,—“let fall thy blade
on vulnerable CRESTS”—but now, like Banquo’s ghost, “the bones are
marrowless.”
These curious fossils were first detected in the quarries at Glammis, by
Sir Charles Lyell, and from their striking resemblance to the cephalic
shield of certain trilobites, were supposed, for a time, to belong to the
class of crustaceans. The beds of Carmylie and Balruddery, yield these
organisms in the greatest abundance. One solitary specimen, a fragment of
two inches in length, of the smaller scaly net-mesh, has been obtained
by me in the gray rock, on the south bank of the Tay. The heads are
uniformly in the best state of preservation; indeed hundreds of these lie
entire, where no part of the body has left the trace of an impression. M.
Agassiz assigns, as the reason of this, the great difference that exists
in the structure of these two parts, and especially in the disproportion
of their dimensions and forms, which would offer a distinct resistance
to the pressure to which the animals must have been exposed. “If, on the
other hand,” he adds, “the heads usually present their superior surface
to us, it is because their inferior surface, the cavity of the mouth,
the branchial arch and sinuosities of the inferior bones of the cranium,
are points of support comparatively more solid, and more adapted for
sustaining the matter which has filtered into them, than a larger surface
slightly convex, which would naturally be detached from the rock wherever
a separation was found in it.”
THE DEN OF BALRUDDERY presents us with a group of very remarkable
fossils, comprising, in an area of the gray sandstone of a few square
yards, innumerable impressions of the plant-markings already noticed,
multitudes of the Cephalaspis, spines, and other ichthyolites, along
with two entirely new genera of fishes of the order of Placoids. The
sandstone here is of a very slaty character, splitting up into thin
layers, betwixt every one of which some organism or other has impressed
its form; and the different kinds are often so promiscuously huddled
together, as to suggest the idea of some violent commotion in the element
which collected and destroyed them. In the “Synoptical Table of British
Fossil Fishes,” by M. Agassiz, we find inserted a _Parexus recurvus_,
and a _Clematius reticulatus_, from this locality; they are represented
simply as ichthyodorulites, no complete specimens of the creatures having
been presented to him, nor indeed have any been as yet obtained. One of
the specimens in the Balruddery collection, when returned by M. Agassiz,
was labeled as a _Palæocarcinus alatus_: and in the 14th Livraison of
his “Poisson Fossiles,” he thus writes:—“Enfin j’en dois aussi plusieurs
espèces à M. Webster de Balruddery. Parmi ses échantillons j’en ai
trouvé plusieurs d’un grand intérêt, parce qu’ils m’ont fait connaître
que le genre Pterygotus que j’avais établi, il y a plusieurs années,
sur des fragmens très-imparfaits, n’appartient point à la classe de
poissons, mais bien en celle des crustaces. Une pareille erreur semble
à peine possible, et cependant elle paraît excusable lorsque je ferai
connaître les caractères de ce fossile; des botanistes célèbres n’avaient
pas hésité à les ranger parmi les Algues. Les Seraphius fossiles
des carrières de Forfarshire, que M. Lyell a soumit à la Section de
Geologie de l’Association Britannique réunie à Edinbourg en 1834, sont
des ces mêmes crustaces gigantesques du terrain Dévonien. Ils offrent
des rapports éloignés avec les Entomestracés gigantesques du terrain
houiller, décrits sous les noms d’Edotea et d’Eurypterus.” The Lobster,
accordingly, of Balruddery is the first discovery of its fossil kind;
portions of nearly every organ of the body have been found, so as to make
the restoration of the crustacean complete: a creature of at least four
feet in length, and as in the fishes of this epoch, the shelly covering
is dotted all over with enameled scale-like markings. This magnificent
collection remains still undescribed, hundreds of the specimens, from
the minute to the gigantic, and of the greatest diversity of character,
being only detached fragments of the structures to which they belonged;
but enough have we there to testify as to the early prolific abundance of
Nature, and that, throughout all ages, her types and forms of life are
wonderfully allied.
The interesting locality of Balruddery is succeeded by another in the
ascending order of the strata, but lower on the plain of the Carse of
Gowrie,—Clashbennie, situated about six miles to the westward. This
rock is well entitled to be denominated the Holoptychius Bed, as here
the first complete specimen of that remarkable genus was obtained, and
of which there are three species in the deposit, namely, H. Giganteus,
Noblissimus, and Murchisoni. Three other genera, of the ganoid order of
fishes, have left their relics in this bed, some of them in a beautiful
state of preservation: these are Glyptosteus reticulatus, Phyllolepis
concentricus, and Glyptolepis elegans, all named and described by M.
Agassiz.
The Holoptychius ranks among the family of Cœlacanthes, and the term
Holoptychius (holos, entire; and ptyche, a wrinkle) is applied to the
fossil from the circumstance of the scales being covered with wrinkled
dots or markings, the enameled surface of which is indented with deep
undulating furrows. Another characteristic feature of this genus consists
in the distant position of the ventrical fins, being considerably removed
toward the tail, and in the arrangement of the branchial organs, which
form two large plates between the branches of the inferior ray, as in
the genus Megalichthys. The structure of the “nageoirs,” the rounded
form of the ventrical fin, and the manner in which the rays of its
anterior edge are insensibly prolonged, in connection with their relative
thinness, are also marked distinctions. The head of the Holoptychius
is remarkably small in comparison with the size of the body, which, in
the Clashbennie specimen measures thirty inches in length by twelve in
breadth. The scales are still disproportionately larger than either the
head or body, some of them being nearly three inches in length by two
and a half in breadth, with a corresponding thickness. The structure
of the dermal covering is beautiful in the extreme; it is composed of
these scale-plates, articulating, and laced together in such a way as
to combine the greatest possible strength with the highest degree of
flexibility; and, protected by a rich coating of enamel, it must have
been capable of the greatest endurance, and of resisting any pressure.
Two thickly set rows of teeth; one inner, and extremely minute, the other
large and pointed, completed the equipments of a mouth adapted to seize
and crush to powder any intruder upon its pasturage. The vertebral column
extended to the extremity of the tail, which was forked or divided into
two unequal lobes, a contrivance of nature that enabled the animal to
turn quickly on its back before striking its prey. This form of the tail
is called the HETEROCERCAL; it is characteristic of most of the fishes
of the period, and prevailed during the palæozoic age; when it gave way,
at the era of the chalk formation, to what is termed the HOMOCERCAL
structure, and which still exists in the fishes of the current epoch.
The Phyllolepis is a very striking genus of the same family, and has
also been noticed at considerable length by the Swiss naturalist. The
scales, or other plates, which covered the body of this fish are of
enormous dimensions, being nearly half a foot in diameter, and rounded
to an obtuse angle. What distinguishes them from all other scales, and
particularly from those of the Holoptychius, with which they have certain
external resemblances, is their extreme tenuity, consisting simply of a
film of enamel spread over a thin osseous membrane, scarcely so thick as
the blade of a knife, and varying from three to five inches in diameter.
Their surface is smooth, or slightly marked with concentric wrinkles
parallel to the edge of the scale. Two species of this genus have been
found, one in the old red, and the other in the coal formation. In the
Clashbennie sandstone only a few detached scales have been detected, but
sufficiently well preserved to show the superposition, or imbrication,
perhaps, in which they stood relatively to each other, the wrinkles
serving as grooves by which their adhesion was more firmly effected. One
decided characteristic of this organ in the _Phyllolepis concentricus_
is, that it is a little raised toward the middle, whence it again
declines or sinks on all sides, after the manner of a roof.
The sandstones flanking the hill of Kinnoul, and stretching along the
left bank of the Tay, by Scone and Lethendy, appear to be a continuation
of the Clashbennie beds, as also those occupying the ridges by Ruthven
and Dupplin, where they assume much of the fissile character and
micaceous aspect of the Carmylie flag-stone, but everywhere destitute of
organic remains in the whole western district from Perth to Callander.
The absence of fossils from particular beds has been accounted for in
various ways. But even in the same series of rocks, and where there is no
break in the continuity of the strata, it is a maxim of geology that the
range of fossils is not always co-extensive with the mineral deposits.
Then, as now, the explanation is, that the slightest physical changes
affected the tastes and habits of the animal kingdom; the direction and
strength of a current; the depth of water; the character and qualities
of the sea-bottom; the force of tidal action; the season of the year,
being, it is well known, singly sufficient to produce great differences
as to the migrations and favorite haunts of almost every aquatic race.
And hence it is laid down as a recognized principle in the science, that
a particular bed of rock within certain limits is not to be excluded
from its place in a system, and another substituted therein, by the mere
presence or absence of a certain class of fossils. Individuals, too, will
often outlive the family to which they belong, and be found in certain
localities intermixed with the races of a higher group of rocks.—And
these remarks are applicable to all the formations, less or more,
from the lowest fossiliferous strata to the latest of the tertiaries.
Applied to the old red sandstone, they serve to explain the fact that,
while the precise relative position of the western beds in the district
under review cannot in every instance be determined, large spaces or
areas are entirely destitute of organic remains which in the eastern,
and not distant, localities are detected in the greatest abundance and
variety. The system of rocks is unquestionably the same, but neither
cephalaspis, parexus, clematius, holoptychius, glyptosteus, phyllolepis,
nor glyptolepis, ever would seem to have frequented these parts; whether
for the reasons above assigned, or for any other local cause, or simply
that they did not like the region—as the grouse and ptarmigan, even now,
will not descend to the plains—is one of the recondite problems of animal
life connected with the new as well as the older state of things. These
beds may yet, however, be discovered to be fossiliferous, as the smallest
space in local distance may reveal their hidden stores, to reward the
diligent observer, and add to our knowledge of the aboriginal fauna of
the district.
The lesson farther taught by the varied phenomena which have passed under
review in this chapter would seem to be, that there is nothing fixed or
permanent in such arrangements of nature.—These are the beginnings of
creation, and both as respects organic and inorganic matter, change and
re-construction have prevailed from the earliest periods to which our
researches can penetrate.—The Divine Architect did not complete things
as we now see them, in one initial act; nor, as we regard quiescence
and stability, were the elements and forces of nature so balanced as
not to interfere even in violent collision with one another. A world is
called into existence. Storms and commotions rend its frame.—Sea and land
contend for mastery. And everything within its bounds, like the flux of
time, like day and night, summer and winter, life and death, is observed
to have emerged into being and form, to have assumed new arrangements,
then to have perished; or gradually, as its nature might be, to have
consumed away.
No reason can be assigned for all this, as the law or order of events,
except the appointment of Him who made and continues the constitution
of nature as it is. No adequate cause of creation can ever be conceived
but that of the Divine Goodness; and while we never can expect fully
to comprehend the wisdom that planned, and the power that carried into
effect, the purposes of that wisdom, still the very effort to attain
knowledge concerning them, fulfills one great object for which man is
made curious about the works of his Maker. In contemplating the wonders
of those days, the variety, adaptation and perfection of everything
in itself as then constructed, he will always refer to that Infinite
Intelligence through whose goodness he is permitted to enjoy knowledge.
In becoming wiser he will become better. His increasing knowledge will be
made subservient to a more exalted faith in that everlasting “Word” who
framed the worlds; and in proportion as the vail becomes thinner through
which he sees the origin and course of things, he will admire all the
more the brightness of Him who was the true light which lighteth every
man that cometh into the world.
[Illustration: Holoptychius Noblissimus.]