Scotland has its four fossil floras,--its flora of the Old Red
Sandstone, its Carboniferous flora, its Oolitic flora, and that flora of
apparently Tertiary age of which his Grace the Duke of Argyll found so
interesting a fragment overflown by the thick basalt beds and trap tuffs
of Mull. Of these, the only one adequately known to the geologist is the
gorgeous flora of the Coal Measures,--probably the richest, in at least
individual plants, which the world has yet seen. The others are all but
wholly unknown; and the Association may be the more disposed to tolerate
the comparative meagreness of the few brief remarks which I purpose
making on two of their number,--the floras of the Old Red Sandstone and
the Oolite,--from the consideration that that meagreness is only too
truly representative of the present state of our knowledge regarding
them; and that if my descriptions be scanty and inadequate, it is only
because the facts are still few. How much of the lost may yet be
recovered I know not; but the circumstance that two great
floras,--remote predecessors of the existing one,--which once covered
with their continuous mantle of green the dry land of what is now
Scotland, should be represented by but a few coniferous fossils, a few
cycadaceous fronds, a few ferns and club mosses, must serve to show what
mere fragments of the past history of our country we have yet been able
to recover from the rocks, and how very much in the work of exploration
and discovery still remains for us to do. We stand on the further edge
of the great floras of by-past creations, and have gathered but a few
handfuls of faded leaves, a few broken branches, a few decayed cones.
The Silurian deposits of our country have not yet furnished us with any
unequivocal traces of a terrestrial vegetation. Professor Nicol of
Aberdeen, on subjecting to the microscope the ashes of a Silurian
anthracite which occurs in Peeblesshire, detected in it minute tubular
fibres, which seem, he says, to indicate a higher class of vegetation
than the algæ; but these may have belonged to a marine vegetation
notwithstanding. I detected some years ago, in the Trilobite-bearing
schists of Girvan, associated with graptolites of the Lower Silurian
type, a vegetable organism somewhat resembling the leaf of one of the
pond weeds,--an order of plants, some of whose species, such as Zostera,
find their proper habitats in salt water. I have placed beside this
specimen a fragment of the same graptolite-bearing rock, across which I
have pasted part of a leaf of _Zostera marina_, the only plant of our
Scottish seas which is furnished with true roots, bears real flowers
inclosed in herbaceous spathes, and produces a well formed farinaceous
seed. It will be seen, that in the few points of comparison which can be
instituted between forms so exceedingly simple, the ancient very closely
resembles the recent organism. It is not impossible, therefore, that
the Silurian vegetable may have belonged to some tribe of plants allied
to Zostera; and if so, we can easily conceive how the Silurian
anthracite of our country may be altogether of marine origin, and may
yet exhibit in its microscopic tubular fibres vestiges of a vegetation
higher than the algæ.
[Illustration: Fig. 117.
_a_, SILURIAN ORGANISM. _b_, GRAPTOLITE. _c_, PORTION OF THE LEAF OF
ZOSTERA MARINA.]
[It were well, in dealing with the very ancient floras, in which
equivocal forms occur that might have belonged to either the land or the
sea, to keep in view those curious plants of the present time, the
habitats of which are decidedly marine, but which are marked by many of
the peculiarities of the seed-bearing plants of the land. The
superiority of Zostera to the common sea weeds of our coasts appears to
have struck in the north of Scotland eyes very little practised in such
matters, and seems to have given rise, in consequence, to a popular
myth. _Zostera marina_ abounds on a series of sand banks, partially
uncovered by the larger stream tides, which lie directly opposite the
town of Cromarty, near the spot pointed out by tradition as the site of
an earlier town, which was swept away some two or three hundred years
ago by the encroachments of the sea. And these banks, with their thick
covering of green Zostera, used to be pointed out by the fishermen of
the place, in my younger days, as the _meadows_ of the old town, still
bearing their original coverings of vegetation,--a vegetation altered no
doubt by the "sea change" that had come over it, but still essentially
the same, it was said, as that which had smiled around the old burgh,
and not at all akin to the brown kelp or tangle that every storm from
the boisterous north-east heaps along the shore. It was virtually
affirmed that the luxuriant terrestrial grasses of ancient Cromarty had
made a virtue of necessity in their altered circumstances; and that,
settling down into grasses of the sea, they remained to testify that an
ancient Cromarty there had _once been_. _Zostera marina_, like most
plants of the land, ripens its seeds towards the close of autumn; and I
have seen a smart night's frost at this season, when coincident with a
stream tide that laid bare the beds, nip its seed-bearing stems by
thousands; and have found them strewed along the beach a few days after,
with all their grass-like spikes fully developed, and their grain-like
seeds charged with a farinaceous substance, which one would scarce
expect to find developed in the sea. In the higher reaches of the
Cromarty Firth, the Zostera beds, which are of great extent, are much
frequented, during the more protracted frosts of a severe winter, by
wild geese and swans, that dig up and feed upon the saccharine roots of
the plant. The Zostera of the warmer latitudes attain to a larger size
than those of our Scottish seas. "A southern species," says Loudon,
"_Zostera oceanica_, has leaves a foot long and an inch broad. It is
used as a thatch, which is said to last a century; bleaches white with
exposure; and furnishes the rush-like material from which the envelops
of Italian liquor flasks are prepared." The simple rectilinear venation
of ribbon-like fronds, usually much broken, that occurs in the Lower Old
Red Sandstone, has often reminded me of that exhibited by this exotic
species of Zostera.]
[Illustration: Fig. 118.
FUCOID.]
[Illustration: Fig. 119.
FUCOIDS.]
Associated with the earliest ichthyic remains of the Old Red Sandstone,
we find vegetable organisms in such abundance, that they communicate
often a fissile character to the stone in which they occur. But,
existing as mere carbonaceous markings, their state of keeping is
usually so bad, that they tell us little else than that the
antiquely-formed fishes of this remote period swam over sea bottoms
darkened by forests of algæ. The prevailing plant was one furnished with
a long, smooth stem, which, though it threw off, in the alternate order,
numerous branches at least half as stout as itself, preserved its
thickness for considerable distances without diminution,--a common
fucoidal characteristic. We find its remains mixed in the rock, though
sparingly, with those of a rough-edged plant, knobbed somewhat like the
thong-like receptacles of _Himanthalia lorea_, which also threw off
branches like the other, but diminished more rapidly. A greatly more
minute vegetable organism of the same beds, characterized by its bifid
partings, which strike off at angles of about sixty, somewhat resembles
the small-fronded variety of _Dictyota dichotoma_, save that the slim
terminations of the frond are usually bent into little hooks, like the
tendrils of the pea just as their points begin to turn. Another rather
rare plant of the period, existing as a broad, irregularly cleft frond,
somewhat resembling that of a modern _Cutleria_ or _Nitophyllum_,
betrays at once, in its outline and general appearance, its marine
origin; as does also an equally rare contemporary, which, judging from
its appearance, seems to have been a true fucus. It exists in the rock
as if simply drawn in Indian ink; for it exhibits no structure, though,
as in some of the ferns of the Coal Measures, what were once the curls
of its leaflets continue to exist as sensible hollows on the surface. It
broadens and divides atop into three or four lobes, and these, in turn,
broaden and divide into minor lobes, double or ternate, and usually
rounded at their terminations. In general appearance the plant not a
little resembles those specimens of _Fucus vesiculosus_ which we find
existing in a diminutive form, and divested of both the receptacles and
the air vessels, at the mouth of rivers. Of two other kinds of plants I
have seen only confused masses, in which the individuals were so crowded
together, and withal so fragmentary and broken, that their separate
forms could not be traced. In the one the general appearance was such as
might be produced by compressed and tangled masses of _Chorda filium_,
in which the linear and even tubular character of the plant could be
determined, but not its continuous, cord-like aspect; in the other, the
fragments seemed well nigh as slim as hairs, and the appearance was such
as might be produced by branches of that common ectocarpus, _E.
littoralis_, which may be seen on our rocky coasts roughening at low
water the stems of laminaria. When highly magnified, a mesial groove
might be detected running along each of the hair-like lines. With these
marine plants we occasionally find large rectilinear stems, resolved
into a true coal, but retaining no organic character by which to
distinguish them. As I have seen some of these more than three inches in
diameter, and, though existing as mere fragments, several feet in
length, they must, if they were also plants of the sea, have exceeded in
size our largest laminaria.[46] And such are the few vegetable
organisms, of apparently aquatic origin, which I have hitherto succeeded
in detecting in the Lower Old Red Sandstone of Scotland.[47] Their
individual numbers, however, must have been very great, though, from the
destructible character of their tissues, their forms have perished in
the stone. The immensely developed flagstones of Caithness seem to owe
their dark color to organic matter mainly of vegetable origin. So
strongly bituminous, indeed, are some of the beds of dingier tint, that
they flame in the fire like slates steeped in oil.
[Illustration: Fig. 120.]
The remains of a terrestrial vegetation in this deposit are greatly
scantier than those of its marine plants; but they must be regarded as
possessing a peculiar interest, as, with the exception of the spore
cases of the Ludlow rocks, the oldest of their class, in at least the
British islands, whose true place in the scale can be satisfactorily
established. In the flagstones of Orkney there occurs, though very
rarely, a minute vegetable organism, which I have elsewhere described as
having much the appearance of one of our smaller ferns, such as the
maidenhair-spleenwort, or dwarf moonwort. It consists of a minute stem,
partially covered by what seems to be a small sheath or hollow bract,
and bifurcates into two fronds or pinnæ, fringed by from ten to twelve
leaflets, that nearly impinge on each other, and somewhat resemble in
their mode of arrangement the leaflets of one of our commonest
Aspleniums,--_Asplenium trichomanes_. One of our highest authorities,
however, in such matters (Professor Balfour of Edinburgh) questions
whether this organism be in reality a fern, and describes it from the
specimen on the table, in the Palæontological chapter of his admirable
Class Book, simply as "a remarkable pinnate frond." (Fig. 13, p. 56.) We
find it associated with the remains of a terrestrial plant allied to
lepidodendron, and which in size and general appearance not a little
resembles one of our commonest club mosses,--_Lycopodium clavatum_.[48]
It sends out its branches in exactly the same style,--some short and
simple, others branched like the parent stem,--in an arrangement
approximately alternate; and is everywhere covered, stem and branch, by
thickly set scale-like leaflets, that, suddenly narrowing, terminate in
exceedingly slim points. It has, however, proportionally a stouter stem
than Lycopodium; its leaves, when seen in profile, seem more rectilinear
and thin; and none of its branches yet found bear the fructiferous stalk
or spike. Its resemblance, however, to this commonest of the
Lycopodia,--a plant that may be gathered by handfuls on the moors by
which the flagstones are covered,--is close enough to suggest a new
reading of the familiar adage on the meeting of extremes. Between the
times of this ancient fossil,--one of the oldest of land plants yet
known,--and those of the existing club moss that now scatters its light
spores by millions over the dead and blackened remains of its remote
predecessor, many creations must have intervened, and many a prodigy of
the vegetable world appeared, especially in the earlier and middle
periods,--Sigillaria, Favularia, Knorria, and Ulodendron,--that have had
no representatives in the floras of latter times; and yet here, flanking
the immense scale at both its ends, do we find plants of so nearly the
same form and type, that it demands a careful survey to distinguish
their points of difference. Here, for instance, to illustrate the fact,
is there a specimen of _Lycopodium clavatum_, from one of these
Caithness moors, that agrees branch for branch, and both in the
disposition of its scales and in general outline, with the specimen in
the stone. What seems to be an early representative of the Calamites
occurs in the same beds. Some of the specimens are of large size,--at
least from nine inches to a foot in circumference,--and retain their
thickness, though existing as fragments several feet in length, with but
little diminution throughout. They resembled the interior casts of
Calamites in being longitudinally furrowed; but the furrows are flatter,
and are themselves minutely striated lengthwise by lines as fine as
hairs; and, instead of presenting any appearance of joints, there run
diagonally across the stems, interrupted and very irregular lines of
knobs. These I find referred to by Dr. Joseph Hooker, in describing a
set of massive but ill preserved remains of the same organism detected
in South Ness quarry, near Lerwick, by the Hon. Mr. Tuffnell, as taking,
in two of the specimens, "the appearance of transverse knobs and bars
(mayhap spirally arranged) that cross the striæ obliquely. But though
the knobs," he adds, "may perhaps indicate a peculiar character of the
plants, they have more probably been caused by pressure during
silicification." As, however, they also occur in the best preserved
fragment of the plant which I have yet seen,--a Thurso specimen which I
owe to my friend Mr. Dick,--I deem it best to regard them, provisionally
at least, as one of the characteristics of the plant. I may mention,
that while I disinterred one of my specimens from the Thurso flagstones,
where it occurred among remains of Dipterus and Asterolepis, I derived
another specimen from the great overlying formation of pale Red
Sandstone to which the lofty hills of Hoy and the tall mural precipices
of Dunnet Head belong; and that this plant is the only organism which
has yet been found in this uppermost member of the Lower Old Red, to at
least the north of the Moray Firth. Another apparently terrestrial
organism of the lower formation, of, however, rare occurrence, very much
resembles a sheathing bract or spathe. It is of considerable size,--from
four to six inches in length, by from two to three inches in
breadth,--of a broadly elliptical and yet somewhat lanceolate form,
deeply but irregularly corrugated, the rugæ exhibiting a tendency to
converge towards both its lower and upper terminations, and with, in
some instances, what seems to be the fragment of a second spathe
springing from its base. Another and much smaller vegetable organism of
the same beds presents the form of a spathe-enveloped bud or unblown
flower wrapped up in its calyx; but all the specimens which I have yet
seen are too obscure to admit of certain determination. I may here
mention, that curious markings, which have been regarded as impressions
made by vegetables that had themselves disappeared, have been detected
during the last twelvemonth in a quarry of the Lower Old Red Sandstone
near Huntly, by the Rev. Mr. Mackay of Rhynie. They are very curious and
very puzzling; but though some of the specimens present the appearance
of a continuous midrib, that throws off, with a certain degree of
regularity, apparent leaflets, I am inclined to regard them rather as
lying within the province of the ichnologist than of the fossil
botanist. They bear the same sort of resemblance to a long,
thickly-leaved frond, like that of the "hard fern," that the cast of a
many-legged annelid does to a club moss; and I was struck, on my first
walk along the Portobello beach, after examining a specimen kindly sent
me by Mr. Mackay, to see how nearly the tract of a small shore crab
(_Carcinus Mænas_) along the wet sand resembled them, in exhibiting what
seemed to be an obscure midrib fringed with leaflets.
But the genuine vegetable organism of the formation, indicative of the
highest rank of any yet found in it, is a true wood of the cone-bearing
order. I laid open the nodule which contains this specimen, in one of
the ichthyolite beds of Cromarty, rather more than eighteen years ago;
but though I described it, in the first edition of my little work on the
Old Red Sandstone, in 1841, as exhibiting the woody fibre, it was not
until 1845 that, with the assistance of the optical lapidary, I
subjected its structure to the test of the microscope. It turned out, as
I had anticipated, to be the portion of a tree; and on my submitting the
prepared specimen to one of our highest authorities,--the late Mr.
William Nicol,--he at once decided that the "reticulated texture of the
transverse section, though somewhat compressed, clearly indicated a
coniferous origin." I may add, that this most ancient of Scottish
lignites presents several peculiarities of structure. Like some of the
Araucarians of the warmer latitudes, it exhibits no lines of yearly
growth; its medullary rays are slender, and comparatively inconspicuous;
and the discs which mottle the sides of its sap-chambers, when viewed in
the longitudinal section, are exceedingly minute, and are ranged, so far
as can be judged in their imperfect state of keeping, in the alternate
order peculiar to the Araucarians. On what perished land of the early
Palæozoic ages did this venerably antique tree cast root and flourish,
when the extinct genera Pterichthys and Coccosteus were enjoying life by
millions in the surrounding seas, long ere the flora or fauna of the
Coal Measures had begun to be?
I may be here permitted to mention, that in a little volume, written in
reply to a widely known and very ingenious work on the Development
hypothesis, I described and figured this unequivocally genuine lignite,
in order to show that a true wood takes its place among the earliest
terrestrial plants known to the geologist. I at the same time
mentioned,--desirous, of course, that the facts of the question should
be fairly stated, whatever their bearing,--that the nodule in which it
occurred had been partially washed out of the fish bed in which I found
it, by the action of the surf; and my opponent, fixing on the
circumstance, insinuated, in the answer with which he honored me, that
it had _not_ belonged to the bed at all, but had been derived from some
other formation of later date. He ought, however, to have taken into
account my further statement, namely, that the same nodule which
enclosed the lignite contained part of another fossil, the well marked
scales of _Diplacanthus striatus_, an ichthyolite restricted, like the
Coccosteus (a specimen of which occurred in a neighboring nodule), to
the Lower Old Red Sandstone exclusively. If there be any value whatever
in palæontological evidence, this Cromarty lignite must have been
deposited in a sea inhabited by the Coccosteus and Diplacanthus. It is
demonstrable that, while yet in the recent state, a Diplacanthus lay
down and died beside it; and the evidence in the case is unequivocally
this, that in the oldest portion of the oldest terrestrial flora yet
known, there occurs the fragment of a tree quite as high in the scale as
the stately Norfolk Island pine, or the noble cedar of Lebanon.
[I have failed hitherto in finding any remains of terrestrial
plant-covered surfaces in the Old Red Sandstone of Scotland, though
decided traces of desiccated sub-ærial ones are not rare. Shallows and
banks seem to have been numerous during the period of at least the Lower
formation. The flagstones of Caithness and Orkney, and the argillaceous
fish beds of Cromarty and Ross, not only abound in the ripple-marked
surfaces of a shallow sea, but also in cracked and flawed planes that
must have dried and split into polygonal partings in the air and the
sun. The appearance of these in the neighborhood of the town of Thurso,
about half a mile to the east of the river, is not a little curious.
Bearing throughout the general dingy hue of the flagstones, they yet
consist of alternating beds of two distinct characters and qualities.
The one kind, fissile, finely grained, and sharply ripple-marked, seems
to have been deposited in shallow water; the other, not fissile, but, if
I may so speak, felted together so as to yield with difficulty to the
hammer in any direction, and traversed by polygonal partings, filled up
usually by the substance of the overlying stratum, appears to have had a
different origin. The state of keeping, too, in which the ichthyic
remains of these alternating beds occur is always very different. The
smaller and more delicately organized fishes are never found entire,
save in the fissile, finely grained beds; in the others we detect only
scattered fragments; and even these, unless they belonged to the robust
Asterolepis or his congeners,--which, however, in these beds they
usually do,--much broken. The polygonal partings seem to indicate that
these toughly-felted beds, whose very style of weathering--rough,
gnarled, fretted into globose protuberances and irregular hollows--shows
that it had not been formed by quiet deposition, must have had their
broad backs raised for a time above the surface of the water, to be
desiccated in the hot sun. And the fragmentary state of the fossils
which they contain seems to point, with the roughnesses of their
weathered surfaces, to some peculiarity in their origin. The
recollection which they awoke in my mind with each visit I paid them for
three years together, may probably indicate what that origin was. I had
a relation who died more than a quarter of a century ago, who passed
many years in British Guiana, in the colony of Berbice, and whose
graphic descriptions of that part of South America made a strong
impression upon me when a boy, and still dwells in my memory. He was
settled on a cotton plantation near the coast side; and so exceedingly
flat was the surrounding country, that the house in which he dwelt,
though nearly two miles distant from the shore, stood little more than
five feet above its level. The soil consisted of a dark gray
consolidated mud; and in looking seawards from the margin of the land,
there was nothing to be seen, when the tide fell, save dreary mud flats
whole miles in extent, with the line of blue water beyond stretching
along the distant horizon. These mud flats were much frequented by birds
of the wader family, that used to come and fish in the shallow pools for
the small fry that had lingered behind when the tide fell; and my
cousin, a keen sportsman in his day, has told me that he used to steal
upon them in his mud shoes,--flat boards attached to the soles, like the
snow shoes of the higher latitudes,--and enjoy rare sport in knocking
down magnificent game, such as "the roseate spoonbill" and "gorgeous
flamingo." There were times, however, when the mud shoe proved of no
avail, and the flat expanse remained impassable for weeks,--
"A boggy syrtis, neither sea
Nor good dry land."
The coast,--directly impinged on by the drift current, and beaten by the
long roll of waves which had first begun to rise under the impulsions of
the trade winds on the African coast two thousand miles away,--was much
exposed to tempests; and after every fresh storm from the east, a huge
bank of mud used to come rolling in from the sea, three or four feet
abreast, and remain wholly impassable until, during some two or three
neap tides, its surface had been exposed to a tropical sun, and
partially consolidated by the heat. And then the waste would become
passable as before, and the chopped and broken surface, exposed to the
ordinary action of the sea, and to gradual depositions during flood,
would begin to be smoothed over, and the birds would find themselves no
longer safe. Now, I am inclined to think that we have here the
conditions necessary to the formation of the Thurso deposits. Let us
suppose, near where Thurso now stands, a wide tract of flat mud banks in
a sea so shallow as to be laid dry at ebb for miles together. Let us
further suppose periods of tranquil deposition or re-arrangement, during
which one ripple-marked stratum is laid quietly down over another, and
the fish, killed by accident, or left stranded by the evaporation of the
little pools, are covered up, like the plants in a botanist's
drying-book, in a state of complete entireness. Let us yet further
suppose great mud banks driven by occasional tempests from the deeper
water beyond, and so heaped up over these sedimentary beds as to be
exposed during even the flood of neap tides to the desiccating
influences of the atmosphere and the sun, until the surface has become
hard as a sun-burned brick, and has chopped into polygonal partings,
with wide rents between. And finally, let us suppose the whole in this
state laid under water at the return of stream tides, and exposed to the
ordinary sedimentary action. Does it not seem probable that the
alternating beds in all their conditions would be given us by such a
process? In the stratum represented by the mud bank, the stone would be
of what I have termed a _felted_, not a fissile character; its organic
remains would exist in a fragmentary and scattered state,--for, torn up
from their places of original deposition, and rolled onwards in the
storm-impelled mud, they could not fail to be broken up and dispersed;
and further, they would be in large part those of bulky deep-sea fishes.
And lastly, the surface of these beds would be polygonally cracked and
flawed, and the wider cracks filled up by the substance of the overlying
strata. And these overlying strata, on the other hand,--the result of
a period of quiet deposition in shallow water,--would be regularly
bedded, and their ichthyic remains, consisting mainly of small littoral
fishes, would be preserved in a state of comparative entireness.
For, however, such numerous repetitions of alternately _felted_
and fissile ripple-marked strata as we find in the neighborhood of
Thurso,--repetitions carried on for hundreds of feet in vertical
extent,--we require yet another condition,--that condition of gradual
subsidence in the general crust which can alone account for the fact so
often pressed upon the geologist in exploring the Coal Measures, that in
deposits thousands of feet in thickness, each stratum in succession had
been laid down in a shallow sea.]
It is a curious circumstance, that the Old Red flagstones which lie
along the southern flanks of the Grampians, and are represented by the
gray stone known in commerce as the Arbroath Pavement, have not, so far
as is yet known, an organism in common with the Old Red flagstones of
the north. I at one time supposed that the rectilinear, smooth-stemmed
fucoid, already described, occurred in both series, as the gray stones
have also their smooth-stemmed, rectilinear, tape-like organism; but the
points of resemblance were too few and simple to justify the conclusion
that they were identical, and I have since ascertained that they were
entirely different plants. The fucoid of the Caithness flagstones threw
off, as I have shown, in the alternate order, numerous ribbon-like
branches or fronds; whereas the ribbon-like fronds or branches of the
Forfarshire plant rose by dozens from a common root, like the fronds of
Zostera, and somewhat resembled a scourge of cords fastened to a handle.
Contemporary with this organism of the gray flagstone formation, and
thickly occupying the planes on which it rests, there occur fragments of
twisted stems, some of them from three to four inches in diameter
(though represented by but mere films of carbonaceous matter), and
irregularly streaked, or rather _wrinkled_, longitudinally, like the
bark of some of our forest trees, though on a smaller scale. With these
we find in considerable abundance irregularly-shaped patches, also of
carbonaceous matter, reticulated into the semblance of polygonal, or, in
some instances, egg-shaped meshes, and which remind one of pieces of ill
woven lace. When first laid open, these meshes are filled each with a
carbonaceous speck; and, from their supposed resemblance, in the
aggregated form, to the eggs of the frog in their albuminous envelop,
the quarriers term them "puddock [frog] spawn." The slabs in which they
occur, thickly covered over with their vegetable impressions, did
certainly remind me, when I first examined them some fifteen years ago,
of the bottom of some stagnant ditch beside some decaying hedge, as it
appears in middle spring, when paved with fragments of dead branches and
withered grass, and mottled with its life-impregnated patches of the
gelid substance regarding which a provincial poet tells his readers, in
classical Scotch, that
"Puddock-spue is fu' o' e'en,
An' every e'e 's a pu-head."[49]
Higher authorities than the quarriers,--among the rest, the late Dr.
Mantell,--have been disposed to regard these polygonal markings as the
fossilized spawn of ancient Batrachians; but there now seems to be
evidence enough from which to conclude that they are the remains, not of
the eggs of an animal, but of the seed of a plant. Such was the view
taken many years ago by Dr. Fleming,--the original discoverer, let me
add, of fossils both in those Upper and Middle Old Red Sandstone
deposits that lie in Scotland to the south of the Grampians. "These
organisms," we find him saying, in a paper published in "Cheek's
Edinburgh Journal" (1831), "occur in the form of circular flat patches,
not equalling an inch in diameter, and composed of numerous smaller
contiguous pieces. They are not unlike what might be expected to result
from a compressed berry, such as the bramble or the rasp. As, however,
they are found adjacent to the narrow leaves of gramineous [looking]
vegetables, and chiefly in clay slate, originally lacustrine silt, it is
probable that they constituted the conglobate panicles of extinct
species of the genus Junicus or Sparzanium." From specimens subsequently
found by Dr. Fleming, and on which he has erected his species _Parka
decipiens_, it seems evident that the nearly circular bodies (which in
all the better preserved instances circumscribe the small polygonal
ones) were set in receptacles somewhat resembling the receptacle or
calyx of the strawberry or rasp. Judging from one of the specimens, this
calyx appears to have consisted of five pieces, which united in a
central stem, and were traversed by broad irregularly diverging striæ.
And the spawn-like patches of Carmylie appear to be simply ill preserved
specimens of this fruit, whatever its true character, in which the
minute circular portions, divested of the receptacle and stem, had been
thrown into irregular forms by the joint agency of pressure and decay.
The great abundance of these organisms,--for so abundant are they, that
visitors to the Carmylie quarries find they can carry away with them as
many specimens as they please,--may be regarded as of itself indicative
of a vegetable origin.[50] It is not in the least strange, however, that
they should have been taken for patches of spawn. The large-grained
spawn of fishes, such as the lump-fish, salmon, or sturgeon, might be
readily enough mistaken, in even the recent state, for the detached
spherical-seed vessels of fruit, such as the bramble-berry, the
stone-bramble, or the rasp. "Hang it!" I once heard a countryman
exclaim, on helping himself at table to a spoonful of Caviare, which he
had mistaken for a sweet-meat, and instantly, according to Milton, "with
sputtering noise rejected,"--"Hang it for nasty stuff!--I took it for
bramble berry jam."
[Illustration: Fig. 121.
PARKA DECIPIENS.]
[Illustration: Fig. 122.]
[Illustration: Fig. 123.]
Along with these curious remains Dr. Fleming found an organism which in
form somewhat resembles the spike of one of the grasses, save that the
better preserved bracts terminate in fan or kidney-shaped leaflets, with
a simple venation radiating from the base. It is probably a fern, more
minute in its pinnules than even our smallest specimens of true
maidenhair. Its stipes, however, seems proportionally stouter than that
of any of the smaller ferns with which I am acquainted. But the state of
keeping of the specimen is not good, nor do I know that another has yet
been found. Further, in the same beds Dr. Fleming found a curious
nondescript vegetable, or rather part of a vegetable, with smooth narrow
stems, resembling those of the smooth-stemmed organism of the Caithness
flagstones, but unlike it in the circumstance that its detached nearly
parallel stalks anastomose with each other by means of cross branches,
that unite them in the middle, somewhat in the style of the Siamese
twins. I have heard the doctor suggest, but know not whether he has
placed the remark on record, that these parallel stems may have been but
the internal fibres of some larger plant, whose more succulent portions
have disappeared; and certainly, while such instances of anastomosis are
rare among the _stems_ of plants, they are common enough among their
_internal fibres_, as all who have examined the macerated _debris_ of a
kitchen-garden or a turnip-field must have had occasion to remark. We
sometimes, however, find cases of anastomosis among the stems of even
the higher plants. I have seen oftener than once, in neglected hawthorn
hedges, the branch of one plant entering into the stem of another, and
becoming incorporated with its substance; and we are told by Professor
Balfour, that this kind of chance adhesion is often seen in the branches
of the ivy; and that not unfrequently, by a similar process, the roots
of contiguous trees are united. Nor does it seem improbable, that what
occasionally takes place among the higher plants of the present time may
have been common among some of the comparatively low plants of so
ancient a period as that of the Middle Old Red Sandstone. This formation
of the gray tilestones has furnished one vegetable organism apparently
higher in the scale than those just described, in a well marked
Lepidodendron, which exhibits, like the Araucarian of the Lower Old Red,
though less distinctly, the internal structure. It was found about
sixteen years ago in a pavement quarry near Clockbriggs,--the last
station on the Aberdeen and Forfar Railway as the traveller approaches
the town of Forfar from the north. I owe my specimen of this ancient
Lepidodendron to Mr. William Miller, banker, Dundee, an accomplished
geologist, who has taken no little trouble in determining its true
history. He has ascertained that it occurred deep in the rock,
seventy-one feet from the surface; that the beds which rested over it
were composed, in the descending order, first, of a conglomerate thirty
feet thick; secondly, of a red rock four feet thick; thirdly, of
twenty-eight feet of the soft shaly substance known to the quarriers as
caulm; and fourthly, of more than nine feet of gray pavement,
immediately under which, in a soft, argillaceous stratum, lay the
organism. It was about four feet in length, bulged out at the lower end
into a bulb-like protuberance, which may have been, however, merely an
accidental result of its state of keeping; and threw off, at an acute
angle, two branches about a foot from the top. It was covered with a
bark of brittle coal, which is, however, wanting in all the fragments
that have been preserved; and was resolved internally into a brown
calcareous substance of about the hardness of ordinary marble, and very
much resembling that into which the petrifactive agencies have
consolidated the fossil trees of Granton and Craigleith. From the
decorticated condition of the surviving fragments, and the imperfect
preservation of the interior structure, in all save the central portions
of its transverse sections, it yields no specific marks by which to
distinguish it; but enough remains in its irregular network of cells,
devoid of linear arrangement, and untraversed by medullary rays, to
demonstrate its generic standing as a Lepidodendron.
[It has been questioned whether the lower place in the Old Red System
should be assigned to the flagstones of Caithness and Ross, with their
characteristic Dipterus and Coccosteus beds, or to the gray tilestones
of Forfar and Kincardineshires, with their equally characteristic
Cephalaspis. The evidence on the point is certainly not so conclusive as
I deemed it fifteen years ago, when our highest authority on the subject
not only regarded the tilestone of the Silurian regions of England as a
member of the Old Red Sandstone (an arrangement which I am still
disposed to deem the true one), but also held further, that there had
been detected in this formation near Downtown Castle, Herefordshire,
broken remains of _Dipterus macrolepidotus_, one of the best marked
ichthyolites of the flagstones of Caithness and Orkney. A great and
unbroken series of fossiliferous rocks, with Dipterus at its base,
Cephalaspis in its medial spaces, and Holoptychius at its top, might
well be regarded as the analogue of the Old Red of Scotland, with the
Caithness flagstones ranged at its bottom, the Cephalaspis beds of
Forfarshire placed in its middle, and the Holoptychius beds of Scot-Crag
and Clashbinnie on its upper horizon; but since that time the tilestones
have been transferred to the Upper Silurian division of rocks, and the
evidence furnished by their supposed Dipterus has not been confirmed.
And as the Old Red Sandstones of Scotland have no true fossiliferous
base, but rest on primary rocks both to the south and north of the
Grampians, it may be regarded as in some degree a moot point whether the
lowest fossiliferous beds to the north be older or newer than those to
the south, or, what is quite possible, of the same age. Provisionally,
however, I have arranged my paper on the supposition that the Coccostean
formation of the north is the lowest and oldest of the three; and this
from the following considerations. In the first place, the Coccosteus
and its contemporaries appear in the north at a very short distance
above the base of the system. I have disinterred an Osteolepis from a
fish bed near Cromarty only thirty-three feet over the great
conglomerate, and only a hundred and twenty-nine feet over the granitic
gneiss beneath; whereas the Cephalaspis beds occur high above the
primary base of the system in the south,--at some distance over even the
thick conglomerate of Stonehaven and Dunnottar; and under this
conglomerate, as shown in the section furnished by the valley of the
North Esk, there lies a pale red sandstone member of the system,
estimated by Colonel Imrie at seven hundred and eighty feet in
thickness. The conglomerate itself he estimates at twelve hundred feet.
Adopting as correct Colonel Imrie's section, taken along the banks of
the North Esk,--and the colonel was unquestionably a truthful
observer,--the Cephalaspis beds of the south lie nearly two thousand
(nineteen hundred and eighty) feet above the Azoic slates on which the
Old Red Sandstone of Forfarshire rests, whereas the Coccosteus and
Osteolepis beds of the north lie only one hundred and twenty-nine feet
over the Azoic gneiss on which the Old Red Sandstone of Cromarty rests.
There is thus at least _room_ in the south for an underlying
fossiliferous formation between that of the Cephalaspis and the base of
the system, but none in the north beneath that of the Coccosteus and its
base. In the north we find the _room_ lying above, between the
Coccostean and Holoptychian formations, and represented by that great
unfossiliferous deposit of pale sandstone to which the hills of Hoy and
the rocks of Duncansbay Head and of Tarbet Ness belong. Further, in the
second place, while the upper or Holoptychian formation is found
_directly_ overlying that of the Coccosteus in only one
locality,--Moray,--we find it directly overlying that of the Cephalaspis
in _two_ widely separated localities;--in the vast band of Old Red which
runs diagonally across the island from sea to sea, parallel to the
Grampian chain, and in the immensely developed Red Sandstones of England
and Wales. And it is of course more probable that the two corroborative
instances should represent the natural succession of the formations, and
the single instance the accidental gap in the scale consequent on the
missing formation, than that, _vice versa_, the solitary instance should
represent the natural succession, while the two mutually corroborative
ones should represent, in localities widely apart, the mere accident of
the gap. But, in the third place, I attach more weight to a conclusion
founded on the positive character of the groups of organic remains by
which the three great formations of the Old Red System are
characterized, than I do to either of these considerations. The
organisms of the Cephalaspian deposits differ _generically_, and in
their whole aspect, from both those of the Coccostean and Holoptychian
formations; whereas the organisms of the Coccostean formations, while
they resemble generically and in the group those of the Holoptychian
one, mainly differ from them _specifically_. The extreme _generic_
difference in the one case argues evidently a great difference in
_condition_,--the lesser specific difference in the other, a great
difference in point _of time_. The Cephalaspian formation might, as a
fresh water formation, be nearly contemporary with either of the other
two, or, as seems more probable, interposed between them; while they
themselves, on the other hand, generically similar and decidedly marine
in their character, must have been so widely separated in time, that all
the species of the lower group became extinct ere those of the upper one
had been ushered into being. And such are some of the considerations
that still lead me, notwithstanding the failure of previous evidence, to
hold, at least, provisionally, that our Scottish flagstones to the north
of the Grampians occupy a lower horizon than our Scottish tilestones to
the south. It must, however, be stated, on the other hand, that the
crustaceans of the gray tilestones of Forfar and Kincardine not a little
resemble those of the Upper Silurian and red tilestone beds of England;
and that, judging from the ichthyodorulites found in both, their fishes
must have been at least generically allied. The crustaceans of the upper
Silurian of Lesmahagow, too, seem certainly much akin to those of the
Forfarshire tilestones.]
[Illustration: Fig. 124.
CYCLOPTERUS HIBERNICUS.]
Above this gray tilestone formation lies the Upper Old Red Sandstone,
with its peculiar group of ichthyic organisms, none of which seem
specially identical with those of either the Caithness or the
Forfarshire beds. For it is an interesting circumstance, suggestive
surely of the vast periods which must have elapsed during its
deposition, that the great Old Red System has, as I have just said, its
three distinct platforms of organic existence, each wholly different
from the others. Generically and in the group, however, the Upper fishes
much more closely resemble, I repeat, the fishes of the Lower or
Caithness and Cromarty platform, than they do those of the Forfarshire
and Kincardine one. The vegetable remains of the Upper formation in
Scotland are both rare and ill preserved. I have seen what I deemed
fucoidal markings dimly impressed on the planes of some of the strata,
not in the carbonaceous form so common in the other two formations, but
as mere colored films of a deeper red than the surrounding matrix.
Further, I have detected in the same beds, and existing in the same
state, fragments of a striated organism, which may have formed part of
either a true calamite, like those of the Coal Measures, or of some such
striated but jointless vegetable as that of the Lower Old Red of Thurso
and Lerwick.[51] With these markings ferns are occasionally found; and
to one of these, from the light which it throws on the true place in the
scale of a series of deposits in a sister country, there attaches no
little interest. I owe my specimen to Mr. John Stewart of Edinburgh, who
laid it open in a micaceous red sandstone in the quarry of Prestonhaugh,
near Dunse, where it is associated with some of the better known
ichthyic organisms of the Upper Old Red Sandstone, such as _Pterichthys
major_ and _Holoptychius Nobilissimus_. Existing as but a deep red film
in the rock, with a tolerably well defined outline, but without trace of
the characteristic venation on which the fossil botanist, in dealing
with the ferns, founds his generic distinctions, I could only determine
that it was either a Cyclopterus or Neuropterus. My collection was
visited, however, by the late lamented Edward Forbes, only a few weeks
before his death; and he at once recognized in my Berwickshire fern, so
unequivocally an organism of the Upper Old Red, the _Cyclopterus
Hibernicus_ of those largely developed beds of yellow sandstone which
form so marked a feature in the geology of the south of Ireland, and
whose true place, whether as Upper Old Red or Lower Carboniferous, has
been the subject of so much controversy. I had been previously
introduced by Professor Forbes, in the Museum of Economic Geology in
Jermyn Street, London, to an interesting collection of plants from these
yellow beds, and had an opportunity afforded me of examining the only
ichthyic organism hitherto found associated with them; and was struck,
though I could not identify its species, with its peculiarly Old Red
aspect; but the evidence of the Cyclopterus is of course more conclusive
than that of the fish; and we may, I think, legitimately conclude, that
in Ireland, as in our own country, it was a contemporary of the great
Pterichthys (_P. major_),--the hugest, and at least one of the last, of
his race,--and gave its rich green to the hill sides of what is still
the Emerald Island during the latter ages of the Old Red Sandstone, and
ere the Carboniferous period had yet begun. The _Cyclopterus
Hibernicus_, as shown both by the Prestonhaugh specimen and those of
Ireland, was a bipinnate fern of very considerable size,--probably a
tree fern. Its pinnæ, opposite in the lower part of the frond, are
alternate in the upper; while its leaflets, which are of a
sub-rhomboidal form, and so closely ranged as to impinge on each other,
are at least generally alternate in their arrangement throughout. Among
living plants it seems most nearly represented by a South American
species,--_Didymocloena pulcherrima_,--one of the smaller tree ferns.
The leaves of this graceful species are bipinnate, like those of the
fossil; and the pinnæ (thickly set with simple, alternately arranged
leaflets) are opposite in the lower part of the frond, and alternate in
the upper. Widely as they are separated in time, the recent South
American Didymocloena and the Old Red Sandstone Cyclopterus, that
passed into extinction ere the times of the Coal, might be ranged
together, so far at least as appears from their forms, as kindred
species. It were very desirable that we had a good monograph of the
Irish Old Red plants, the contemporaries of the latter, as the
completest and best preserved representatives of the Middle Palæozoic
flora yet found. Sir Roderick Murchison has figured a single pinnæ of
this Cyclopterus in his recently published "Siluria;" and Sir Charles
Lyell, both that and one of its contemporary Lepidodendra, in the last
edition of his "Elements." These interesting fragments, however, serve
but to excite our curiosity for more. When urging Professor Edward
Forbes on the subject, ere parting from him for, alas! what proved to be
the last time, he intimated an intention of soon taking it up; but I
fear his purposed monograph represents only one of many works, important
to science, which his untimely death has arrested for mayhap long years
to come.
In the uppermost beds of the Upper Old Red formation in Scotland, which
are usually of a pale or light yellow color, the vegetable remains again
become strongly carbonaceous, but their state of preservation continues
bad,--too bad to admit of the determination of either species or genera;
and not until we rise a very little beyond the system do we find the
remains of a flora either rich or well preserved. But very remarkable is
the change which at this stage at once occurs. We pass at a single
stride from great poverty to great wealth. The suddenness of the change
seems suited to remind one of that experienced by the voyager,
when,--after traversing for many days some wide expanse of ocean,
unvaried save by its banks of floating sea weed, or, where occasionally
and at wide intervals, he picks up some leaf-bearing bough, or marks
some fragment of drift weed go floating past,--he enters at length the
sheltered lagoon of some coral island, and sees all around the deep
green of a tropical vegetation descending in tangled luxuriance to the
water's edge,--tall, erect ferns, and creeping lycopodiaceæ, and the
pandanus, with its ærial roots and its screw-like clusters of narrow
leaves, and, high over all, tall palms, with their huge pinnate fronds,
and their curiously aggregated groups of massive fruit. And yet the
more meagre vegetation of the earlier time is not without its special
interest. The land plants of the Old Red Sandstone seem to compose, all
over the world, the most ancient of the terrestrial floras. It was held
only a few years ago, that the Silurians of the United States had their
plants allied to the Lepidodendron. But the group in which these occur
has since been transferred from the Upper Silurian to the Old Red
System; and we find it expressly stated by Professor H. D. Rogers, in
his valuable contribution to the "Physical Atlas" (second edition,
1856), that "the Cadent [or Lower Old Red] strata are the oldest
American formations in which remains of a true terrestrial vegetation
have yet been discovered." It has been shown, too, by Sir Roderick
Murchison, that the supposed Silurian plants of Oporto are in reality
Carboniferous, and owe their apparent position to a reverse folding of
the strata. I have already referred to the solitary spore-cases of the
Ludlow Rocks; and beneath these rocks, says Sir Roderick (1854), "no
remains of plants have been discovered which are recognizably of
terrestrial origin." Scanty, too, as the terrestrial flora of the Old
Red Sandstone everywhere is, we find it exhibiting very definitely the
leading Palæozoic features. Its prevailing plants are the ferns and
their apparent allies. It has in our own country, as has been just
shown, its ferns, its lepidodendra, its striated plants allied to the
calamites, and its decided araucanite; in America, in the Cadent series,
it had its "plants allied to ferns and lepidodendra;" and in the
Devonian basin of Sabero in Spain, its characteristic organisms are, a
lepidodendron (_L. Chemungensis_), and a very peculiar fern
(_Sphenopteris laxus_).[52] But while in its main features it resembled
the succeeding flora of the Carboniferous period, it seems in all its
forms to have been specifically distinct. It was the independent flora
of an earlier creation than that to which we owe the coal. For the
meagreness of the paper in which I have attempted to describe it as it
occurs in Scotland, I have but one apology to offer. My lecture contains
but little; but then, such is the scantiness of the materials on which I
had to work, that it could not have contained much: if, according to the
dramatist, the "amount be beggarly," it is because the "boxes are
empty." Partly, apparently, from the circumstance that the organisms of
this flora were ill suited for preservation in the rocks, and partly
because, judging from what appears, the most ancient lands of the globe
were widely scattered and of narrow extent, this oldest of the floras is
everywhere the most meagre.
LECTURE TWELFTH.
ON THE LESS KNOWN FOSSIL FLORAS OF SCOTLAND.