reference to all the greater divisions of the animal kingdom, has often
appeared to me a surpassingly wonderful one. We can see but imperfectly,
in those twilight depths to which all such subjects necessarily belong;
and yet at times enough does appear to show us what a very superficial
thing infidelity may be. The general advance in creation has been
incalculably great. The lower divisions of the vertebrata preceded
the higher;—the fish preceded the reptile, the reptile preceded the
bird, the bird preceded the mammiferous quadruped, and the mammiferous
quadruped preceded man. And yet, is there one of these great divisions
in which, in at least some prominent feature, the present, through this
mysterious element of degradation, is not inferior to the past? There
was a time in which the ichthyic form constituted the highest example
of life; but the seas during that period did not swarm with fish of the
degraded type. There was, in like manner, a time when all the carnivora
and all the herbivorous quadrupeds were represented by reptiles; but
there are no such magnificent reptiles on the earth now as reigned over
it then. There was an after time, when birds seem to have been the sole
representatives of the warm-blooded animals; but we find, from the prints
of their feet left in sandstone, that the tallest men might have
“Walked under their huge legs, and peeped about.”
Further, there was an age when the quadrupedal mammals were the magnates
of creation; but it was an age in which the sagacious elephant, now
extinct, save in the comparatively small Asiatic and African circles, and
restricted to two species, was the inhabitant of every country of the Old
World, from its southern extremity to the frozen shores of the northern
ocean; and when vast herds of a closely allied and equally colossal genus
occupied its place in the New. And now, in the times of the high-placed
human dynasty,—of those formally delegated monarchs of creation, whose
nature it is to look behind them upon the past, and before them, with
mingled fear and hope, upon the future,—do we not as certainly see the
elements of a state of ever-sinking degradation, which is to exist for
ever, as of a state of ever-increasing perfectibility, to which there is
to be no end? Nay, of a higher race, of which we know but little, this
much we at least know, that they long since separated into two great
classes,—that of the “elect angels,” and of “angels, that kept not their
first estate.”
EVIDENCE OF THE SILURIAN MOLLUSCS—OF THE FOSSIL FLORA. ANCIENT TREE.
After dwelling at such length on the earlier fishes, it may seem scarce
necessary to advert to their lower contemporaries the mollusca,—that
great division of the animal kingdom which Cuvier places second in the
descending order, in his survey of the entire series, and first among the
invertebrates; and which Oken regards as the division out of which the
immediately preceding class of the vertebral animals have been developed.
“The fish,” he says, “is to be viewed as a mussel, from between whose
shells a monstrous abdomen has grown out.” There is, however, a
peculiarity in the molluscan group of the Silurian system, to which I
must be permitted briefly to refer, as, to employ the figure of Sterne,
it presents “two handles” of an essentially different kind, and as in all
such two-handled cases, the mere special pleader is sure to avail himself
of only the handle which best suits his purpose for the time.
Cuvier’s first and highest class of the molluscs is formed of what are
termed the Cephalopods,—a class of creatures possessed of great freedom
of motion: they can walk, swim, and seize their prey; they have what even
the lowest fishes such as the lancelet, want,—a brain enclosed in a
cartilaginous cavity in the head, and perfectly formed organs of sight;
they possess, too, what is found in no other mollusc,—organs of hearing;
and in sagacity and activity they prove more than matches for the smaller
fishes, many of which they overmaster and devour. With this highest
class there contrasts an exceedingly low molluscous class at the bottom
of the scale, or, at least, at what is now the bottom of the scale; for
they constitute Cuvier’s _fifth_ class; while his _sixth_ and last, the
Cirrhopodes, has been since withdrawn from the molluscs altogether,
and placed in a different division of the animal kingdom. And this low
class, the Brachiopods, are creatures that, living in bivalve shells,
unfurnished with spring hinges to throw them open, and always fast
anchored to the same spot, can but thrust forth, through the interstitial
chinks of their prison-houses, spiral arms, covered with cilia, and
winnow the water for a living. Now, it so happens that the molluscan
group of the Silurian system is composed chiefly of these two extreme
classes. It contains some of the other forms; but they are few in number,
and give no character to the rocks in which they occur. There was nothing
by which I was more impressed, in a visit to a Silurian region, than that
in its ancient graveyards, as in those of the present day, though in a
different sense, the high and the low should so invariably meet together.
It is, however, not impossible that, in even the present state of things,
a similar union of the extreme forms of the marine mollusca may be taking
place in deep-sea deposits. Most of the intermediate forms provided
with shells capable of preservation, such as the shelled Gasteropoda
and the Conchifers, are either littoral, or restricted to comparatively
small depths; whereas the Brachiopoda are deep-sea shells; and the
Cephalopoda may be found voyaging far from land, in the upper strata
of the sea above them. Even in the seas that surround our own island,
the Brachiopodous molluscs—terebratula and crania—have been found, ever
since deep-sea dredging became common, to be not very rare shells; and in
the Mediterranean, where they are less rare still, fleets of Argonauts,
the representatives of a highly organized family of the Cephalopods, to
which it is now believed the Bellerophon of the Palæozoic rocks belonged,
may be seen skimming along the surface, with sail and oar, high over the
profound depths in which they lie. And, of course, when death comes, that
comes to high and low, the remains of both Argonauts and Brachiopods
must lie together at the bottom, in beds almost totally devoid of the
intermediate forms.
Now, the author of the “Vestiges,” in maintaining his hypothesis,
suspends it on the handle furnished him by the immense abundance of the
Silurian Brachiopods. The Silurian period, he says, exhibits “a scanty
and most defective development of life; so much so, that Mr. Lyell calls
it, _par excellence_, the age of Brachiopods, with reference to the by
no means exalted bivalve shell-fish which forms its predominant class.
Such being the actual state of the case, I must persist in describing
even the fauna of this age, which we now know was not the first, as,
generally speaking, such a humble exhibition of the animal kingdom as
we might expect, upon the development theory, to find at an early stage
of the history of organization.” The reader will at once discern the
fallacy here. The Silurian period was peculiarly an age of Brachiopods,
for in no other period were Brachiopods so numerous, specifically or
individually, or of such size or importance; whereas it was not _so
peculiarly_ an age of Cephalopods, for these we find introduced in still
greater numbers during the Liasic and Oolitic periods. In 1848, when
Professor Edward Forbes edited the Palæontological map of Britain and
Ireland, which forms one of the very admirable series of “Johnstone’s
Physical Atlas,” the Cephalopods of the Silurian rocks of England and
Wales were estimated at forty-eight species, and the Brachiopods at
one hundred and fifty; whereas at the same date there were two hundred
and five Cephalopods of the Oolitic formations enumerated, and but
fifty-four Brachiopods. It is the molluscs of the inferior, not those
of the superior class, that constitute (with their contemporaries the
Trilobites) the characteristic fossils of the Silurian rocks; and hence
the propriety of the distinctive name suggested by Sir Charles Lyell.
But in the development question, what we have specially to consider is,
not the _numbers_ of the low, but the _standing_ of the high. A country
may be distinctively a country of flocks and herds, or a country of
the carnivorous mammalia, or, like New South Wales or the Galapagos, a
country of marsupial animals or of reptiles. Its human inhabitants may
be merely a few hunters or shepherds, too inconsiderable in numbers, and
too much like their brethren elsewhere, to give it any peculiar standing
as a home of men. But in estimating the highest point in the scale to
which the animal kingdom has attained within its limits, it is of its few
men, not of its many beasts, that we must take note. And the point to be
specially decided regarding the organisms of the Silurian system, in this
question, is, not the proportion in _number_ which the lower forms bore
to the higher, but the exact _rank_ which the higher bore in the scale
of existence. Did the system furnish but a single Cephalopod or a single
fish, we would yet have as certainly to determine that the chain of being
reached as high as the Cephalopod or the fish, as if the remains of these
creatures constituted its most abundant fossils. The chain of animal
life reached quite as high on the evening of the sixth day of creation,
when the human family was restricted to a single pair, as it does now,
when our statists reckon up by millions the inhabitants of the greater
capitals of the world; and the special pleader who, in asserting the
contrary, would insist on determining the point, not by the _rank_ of the
men of Eden, but by the _number_ of minnows or sticklebacks that swarmed
in its rivers, might be perhaps deemed ingenious in his expedients, but
certainly not very judicious in the use of them. It is worthy of remark,
however, that the Brachiopods of those Palæozoic periods in which the
group occupied such large space in creation, consisted of greatly larger
and more important animals than any which it contains in the present day.
It has yielded to what geological history shows to be the common fate,
and sunk into a state of degradation and decline.
The geological history of the vegetable, like that of the animal kingdom,
has been pressed into the service of the development hypothesis; and
certainly their respective courses, both in actual arrangement and in
their relation to human knowledge, seem wonderfully alike. It is not
much more than twenty years since it was held that no exogenous plant
existed during the Carboniferous period. The frequent occurrence of
Coniferæ in the Secondary deposits had been conclusively determined
from numerous specimens; but, founding on what seemed a large amount of
negative evidence, it was concluded that, previous to the Liasic age,
nature had failed to achieve a tree, and that the rich vegetation of the
Coal Measures had been exclusively composed of magnificent immaturities
of the vegetable kingdom,—of gigantic ferns and club-mosses, that
attained to the size of forest trees, and of thickets of the swamp-loving
horsetail family of plants, that well nigh rivalled in height those
forests of masts which darken the rivers of our great commercial cities.
Such was the view promulgated by M. Adolphe Brongniart; and it may be
well to remark that, so far as the evidence on which it was based was
positive, the view was sound. It _is_ a fact, that inferior orders of
plants were developed in those ages in a style which, in their present
state of degradation, they never exemplify: they took their place, not,
as now, among the pigmies and abortions of creation, but among its
tallest and goodliest productions. It is, however, _not_ a fact that they
were the highest vegetable forms of their time. True exogenous trees
also existed in great numbers and of vast size. In various localities
in the coal fields of both England and Scotland,—such as Lennel Braes
and Allan Bank in Berwickshire, High-Heworth, Fellon, Gateshead, and
Wideopen near Newcastle-upon-Tyne, and in quarries to the west of the
city of Durham,—the most abundant fossils of the system are its true
woods. In the quarry of Craigleith, near Edinburgh, three huge trunks
have been laid open during the last twenty years, within the space of
about a hundred and fifty yards, and two equally massy trunks, within
half that space, in the neighboring quarry of Granton, all low in the
Coal Measures. They lie diagonally athwart the strata,—at an angle of
about thirty,—with the nether and weightier portion of their boles
below, like snags in the Mississippi; and we infer, from their general
direction, that the stream to which they reclined must have flowed from
nearly north-east to south-west. The current was probably that of a
noble river, which reflected on its broad bosom the shadow of many a
stately tree. With the exception of one of the Granton specimens, which
still retains its strong-kneed roots, they are all mere portions of
trees, rounded at both ends as if by attrition or decay; and yet one
of these portions measures about six feet in diameter by sixty-one feet
in length; another four feet in diameter by seventy feet in length; and
the others, of various thickness, but all bulky enough to equal the
masts of large vessels, range in length from thirty-six to forty-seven
feet. It seems strange to one who derives his supply of domestic fuel
from the Dalkeith and Falkirk coal-fields, that the Carboniferous
flora could ever have been described as devoid of trees. I can scarce
take up a piece of coal from beside my study fire, without detecting
in it fragments of carbonized wood, which almost always exhibit the
characteristic longitudinal fibres, and not unfrequently the medullary
rays. Even the trap-rocks of the district enclose, in some instances,
their masses of lignite, which present in their transverse sections,
when cut by the lapidary, the net-like reticulations of the coniferæ.
The fossil botanist, who devoted himself chiefly to the study of
microscopic structure, would have to decide, from the facts of the case,
not that trees were absent during the Carboniferous period, but that,
in consequence of their having been present in amazing numbers, their
remains had entered more palpably and extensively into the composition
of coal than those of any other vegetable.[32] So far as is yet known,
they all belonged to the two great divisions of the coniferous family,
araucarians and pines. The huge trees of Craigleith and Granton were of
the former tribe, and approximate more nearly to _Altingia excelsa_, the
Norfolk-Island pine,—a noble araucarian, that rears its proud head from a
hundred and sixty to two hundred feet over the soil, and exhibits a green
and luxuriant breadth of foliage rare among the Coniferæ,—than any other
living tree.
[Illustration: Fig. 53.
ALTINGIA EXCELSA, (NORFOLK-ISLAND PINE.)
_From a young specimen in the Botanic Garden, Edinburgh._]
Beyond the Coal Measures terrestrial plants become extremely rare. The
fossil botanist, on taking leave of the lower Carboniferous beds, quits
the land, and sets out to sea; and it seems in no way surprising, that
the specimens which he there adds to his herbarium should consist mainly
of _Fucaceæ_ and _Conferveæ_. The development hypothesis can borrow no
support from the simple fact, that while a high terrestrial vegetation
grows upon dry land, only algæ grow in the sea; and even did the Old Red
Sandstone and Silurian systems furnish, as their vegetable organisms,
fucoids exclusively, the evidence would amount to no more than simply
this, that the land of the Palæozoic periods produced plants of the land,
and the sea of the Palæozoic periods produced plants of the sea.
In the Upper Old Red Sandstone,—the formation of the _Holoptychius_
and the _Stagonolepis_,—the only vegetable remains which I have yet
seen are of a character so exceedingly obscure and doubtful, that all
I could venture to premise regarding them is, that they _seem_ to be
the fragments of sorely comminuted fucoids. In the formation of the
Middle Old Red,—that of the Cephalaspis and the gigantic lobster of
Carmylie,—the vegetable remains are at once more numerous and better
defined. I have detected among the gray micaceous sandstones of
Forfarshire a fucoid furnished with a thick, squat stem, that branches
into numerous divergent leaflets or fronds, of a slim parallelogrammical,
grass-like form, and which, as a whole, somewhat resembles the scourge
of cords attached to a handle with which a boy whips his top. And
Professor Fleming describes a still more remarkable vegetable organism
of the same formation, “which, occurring in the form of circular, flat
patches, composed each of numerous smaller contiguous circular pieces, is
altogether not unlike what might be expected to result from a compressed
berry, such as the bramble or rasp.” In the Lower Old Red,—the formation
of the _Coccosteus_ and _Cheiracanthus_,—the remains of fucoids are more
numerous still. There are gray slaty beds among the rocks of Navity, that
owe their fissile character mainly to their layers of carbonized weed;
and “among the rocks of Sandy-Bay, near Thurso,” says Mr. Dick, “the
dark impressions of large fucoids are so numerous, that they remind one
of the interlaced boughs and less bulky pine-trunks that lie deep in our
mosses.” A portion of a stem from the last locality, which I owe to Mr.
Dick, measures three inches in diameter; but the ill-compacted cellular
tissue of the algæ is but indifferently suited for preservation; and so
it exists as a mere coaly film, scarcely half a line in thickness.
The most considerable collection of the Lower Old Red fucoids which
I have yet seen is that of the Rev. Charles Clouston of Sandwick, in
Orkney,—a skilful cultivator of geological science, who has specially
directed his palæontological inquiries on the vegetable remains of the
flagstones of his district, as the department in which most remained
to be done; but his numerous specimens only serve to show what a
poverty-stricken flora that of the ocean of the Lower Old Red Sandstone
must have been. I could detect among them but two species of plants;—the
one an imperfectly preserved vegetable, more nearly resembling a
club-moss than aught else which I have seen, but which bore on its
surface, instead of the well-marked scales of the _Lycopodiaceæ_,
irregular rows of tubercles, that, when elongated in the profile, as
sometimes happens, might be mistaken for minute, ill-defined leaves;
the other, a smooth-stemmed fucoid, existing on the stone in most cases
as a mere film, in which, however, thickly-set longitudinal fibres are
occasionally traceable, and which may be always distinguished from the
other by its sharp-edged outline, and from the circumstance that its
stems continue to retain the same diameter for considerable distances,
after throwing off at acute angles numerous branches nearly as bulky
as themselves. In a Thurso specimen, about two feet in length, which I
owe to the kindness of Mr. Dick, there are stems continuous throughout,
that, though they ramify in that space into from six to eight branches,
are nearly as thick atop as at bottom. They are the remains, in all
probability, of a long, flexible weed, that may have somewhat resembled
those fucoids of the intertropical seas, which, streaming slantwise
in the tide, rise not unfrequently to the surface in from fifteen to
twenty fathoms of water; and as, notwithstanding their obscurity,
they are among the most perfect specimens of their class yet found,
and contrast with the stately araucarians of the Coal Measures, in a
style which cannot fail to delight the heart of every assertor of the
development hypothesis, I present them to the reader from Mr. Dick’s
specimen, in a figure (fig. 54) which, however slight its interest, has
at least the merit of being true. The stone exhibits specimens of the two
species of Mr. Clouston’s collection,—the sharp-edged, finely-striated
weed, _a_, and that roughened by tubercles, _b_; which, besides the
distinctive character manifested on its surface, differs from the other
in rapidly losing breath with every branch which it throws off, and,
in consequence, runs soon to a point. The cut on the opposite page
(fig. 55) represents not inadequately the cortical peculiarities of
the two species when best preserved. The surface of the tubercled one
will perhaps remind the Algologist of the knobbed surface of the thong
or receptacle of _Himanthalia lorea_, a recent fucoid, common on the
western coast of Scotland, but rare on the east. An Orkney specimen
lately sent me by Mr. William Watt, from a quarry at Skaill, has much
the appearance of one of the smaller ferns, such as the moor-worts, sea
spleen-worts, or maiden-hairs. It exists as an impression in diluted
black, on a ground of dark gray, and has so little sharpness of outline,
that, like minute figures in oil-paintings, it seems more distinct when
viewed at arm’s length than when microscopically examined; but enough
remains to show that it must have been a terrestrial, not a marine
plant. The accompanying print (fig. 56) may be regarded as no unfaithful
representation of this unique fossil its state of imperfect keeping.
The vegetation of the Silurian system, from its upper beds down till
where we reach the zero of life, is, like that of the Old Red Sandstone,
almost exclusively fucoidal. In the older fossiliferous deposits of the
system in Sweden, Russia, the Lake Districts of England, Canada, and
the United States, fucoids occur, to the exclusion, so far as is yet
known, of every other vegetable form; and such is their abundance in some
localities, that they render the argillaceous rocks in which they lie
diffused, capable of being fired as an alum slate, and exist in others
as seams of a compact anthracite, occasionally used as fuel. They also
occur in those districts of Wales in which the place and sequence of the
various Silurian formations were first determined, though apparently
in a state of keeping from which little can be premised regarding
their original forms. Sir Roderick Murchison sums up his notice of the
vegetable remains of the system in the province whence it derives its
name, by stating that he had submitted his specimens to “Mr. Robert Brown
and Dr. Greville, and that neither of these eminent botanists were able
to say much more regarding them than that they were fucoid-like bodies.”
[Illustration: Fig. 54.
FUCOIDS OF THE LOWER OLD RED SANDSTONE.
a. _Smooth-stemmed species._
b. _Tubercled species._
(One sixth nat. size, linear.)]
[Illustration: Fig. 55.
a. _Smooth-stemmed species._
b. _Tubercled species._
(Natural size.)]