beautiful specimens of siliceous petrifactions--that is, animal and
vegetable remains transmuted into silex or flint--are figured in
the subjoined plates, that it may be useful to offer a few remarks
on this subject.[112] In many instances the organic remains in
chalk-flints are simply incrusted by the silex; such is the state
of numerous sponges which are as it were invested by the flint, and
have all their pores and tubes filled up by the same material, the
original tissue appearing as a brown calcareous substance. In other
examples, the sponge has been enveloped in a mass of liquid flint,
and has subsequently perished and decomposed; in this manner have
been formed those hollow nodules, which on being broken present a
cavity containing only a little white powder, or some fragments of
silicified sponge; in many instances the cavity is lined with quartz
crystals, or mammillated chalcedony. Frequently but part of the
zoophyte is permeated by the silex, and the other portion is in the
state of a friable calcareous earth imbedded in the chalk. Sponges
and other zoophytes often form the nuclei of the flint nodules; the
original substance of the organic body being in general silicified,
and the most delicate internal structure preserved. Shells, corals,
and the minute cases of foraminifera, are often immersed as it were
in pure flint, appearing as if preserved in a semi-transparent medium.
[Footnote 112: See Wonders of Geology, vol. i. pp. 74-105, for a
general view of the process of petrifaction.]
But there are innumerable flint nodules in which no traces of
spongeous tissue are apparent, and veins, dikes, and sheets of
tabular flint, that are in a great measure free from organic remains;
containing only such as may be supposed to have become imbedded in a
stream of fluid silex that flowed over a sea-bottom. Wood perforated
by lithodomi and silicified, is occasionally met with; and fuci or
algæ are sometimes found, appearing as if floating in the liquid
flint.
For the most part, the minute shells in the chalk and flint are
filled with amorphous mineral matter; but in many examples, (as
I have ascertained by direct experiment,) the soft parts of
foraminifera remain in the shell.
XII. Foraminifera.--Plate LXII. contains figures of several species
belonging to various genera of those minute fossil shells, the
discoidal involute forms of which were once considered to belong
to the Cephalopoda, and to be related to the Nautilus, Spirula,
&c., but which are now grouped in one family, under the name of
_Foraminifera_; a term derived from the foramina or perforations with
which their shells are traversed, and which have relation to the
peculiar organization of the animals.
Since microscopic observations have become so general, thanks to
the genius and enthusiasm of Ehrenberg, these fossil bodies have
acquired a degree of interest and importance, unsurpassed by more
obvious organic remains. Whole mountain chains and extensive tracts
of country are now known to be almost entirely composed of the
aggregated shells of a few genera of these _microzoa_.[113] In other
deposits their remains are associated with those of _Infusoria_,[114]
(both animal and vegetable,) still more infinitesimal. As much
error prevails among collectors as to the real nature of the fossil
foraminifera, I am induced to annex the following remarks.[115]
[Footnote 113: A convenient term to express animal organisms that can
only be distinctly examined by the aid of the microscope: strata in a
great measure composed of such fossil remains may be distinguished as
_microzoic_ deposits.]
[Footnote 114: This term was first employed to denote the various
minute forms of animal organization that appear in vegetable
infusions; as Rotifers, Monads, Vorticella, &c. But with these,
numerous vegetable forms generally appear, as Gaillonella,
Bacellaria, Navicula, &c.: these were formerly also regarded as
animals, and were consequently comprised under the same general
appellation.]
[Footnote 115: The best scientific account of these animals will be
found in M. D'Orbigny's work on the "Foraminifères Fossiles du Bassin
Tertiaire de Vienne, (Autriche)." Paris, 1846. 1 vol. 4to, with
plates.]
The foraminifera are marine animals of low organization, and, with
but few exceptions, extremely minute: in an ounce of sea-sand between
three and four millions have been distinctly enumerated. When living,
they are not aggregated, but always individually distinct; they are
composed of a body (or vital mass) of a gelatinous consistence, which
is either entire, and round, or divided into segments, placed either
on a simple or alternate line, or coiled spirally, or involuted
round an axis. This body is covered with an envelope or shell, which
is generally testaceous, rarely cartilaginous, and is modelled on
the segments, and follows all the modifications of form and contour
of the body. From the extremity of the last segment, there issue,
sometimes from one, sometimes from several openings of the shell,
or through numerous pores or foramina, very elongated, slender,
contractile, colourless filaments, more or less divided and ramified,
serving for prehension, and capable of entirely investing the shell.
The body varies in colour, but is always identical in individuals of
the same species,--it is yellow, fawn-coloured, red, violet, blue,
&c. Its consistence is variable; it is composed of minute globules,
the aggregation of which determines the general tint. It is sometimes
entire, round, and without segments, as in _Gromia_, _Orbulina_, &c.,
which represent, at all ages, the embryonic state of all the other
genera. They increase, without doubt, by the entire circumference.
When the body is divided by lobes or segments, the primary lobe,
as in the permanent condition of the Gromia, is at first round or
oval, according to the genus; once formed it never enlarges, but is
enveloped externally by testaceous matter; it may be compared to a
ball on which is applied a second larger one, then a third still
larger, and so on during the life of the animal.
The annexed figure of the animal of _Nummulina_ (as given by MM.
Joly and Leymerie) will serve to convey a general idea of the living
Foraminifera.
[Illustration: THE ANIMAL OF THE NUMMULINA.]
The segments, as the body increases, are agglomerated in six
different ways, and these modifications are the basis of M.
D'Orbigny's classification. The discoidal forms, as the _Rotalia_,
_Rosalina_, _Cristellaria_, &c. are involuted like the nautilus,
and divided by septa or partitions, the different lobes of the body
occupying contemporaneously every chamber, and being connected by a
tube or canal that extends through the entire series. In the spiral
forms, the _Textilaria_, &c. the same structure is apparent. These
two groups are the most abundant in the cretaceous strata; many beds
of the white chalk consist almost wholly of the aggregated shells
of the Rosalinæ, Rotaliæ, and Textilariæ.[116] Whatever the form of
the body, the filaments always consist of a colourless matter as
transparent as glass; they elongate from the base to six times the
diameter of the shell. They often divide and subdivide, so as to
appear branched. Though alike in form in the different genera, they
vary much in their position. In some they form a bundle which issues
from a single opening, and is withdrawn into the same by contraction;
in others the filaments project only through each of the pores in
the shell which covers the last segment; in others they issue from
both the large aperture and the foramina. In fine, these filaments or
pseudopodia fulfil in the foraminifera the functions of the numerous
tentacula in the Asteriadæ, or Star-fishes, serving as instruments of
locomotion and attachment.
[Footnote 116: See Wonders of Geology, p. 299]
Neither organs of nutriment nor of reproduction have been detected.
In the genera having one large aperture from which the filaments
issue and retract, we can conceive nutriment to be absorbed by that
opening; but this cannot be the case in the species which have
the last cell closed up; in these the filaments issuing through
the foramina are probably also organs of nutrition. M. D'Orbigny
considers the Foraminifera as constituting a distinct class in
zoology; less complicated than the Echinoderms and the Polypiaria in
their internal organization, they have by their filaments the mode of
locomotion of the first, and by their free, individual existence--not
aggregated and immovably fixed--they are more advanced in the scale
of being than the latter. To me they appear to be merely hydra-form
polypes of the most simple structure, protected by shells;[117] those
composed of different segments, I conceive to be a single aggregated
individual, and not a successive series of beings.
[Footnote 117: An admirable paper on the "_Polystomella crispa_," by
Mr. Williamson, of Manchester, (Trans. Micros. Society of London,
vol. ii.) should be consulted on this question.]
The white chalk is well known to be largely composed of a few kinds
of foraminifera, but the occurrence of the soft bodies of these
animalcules in a fossil state was first discovered by me, in 1845,
in chalk-flints, and was announced in a paper, read before the
Geological Society, entitled, "_Notes of a Microscopical Examination
of Chalk and Flint_."[118] This statement was regarded by some
eminent palæontologists as so "startling and unsatisfactory," that I
resumed the investigation, and communicated the result to the Royal
Society, in a memoir "_On the Fossil Remains of the Soft Parts of
Foraminifera discovered in the Chalk and Flint of the South-East of
England_;"[119] and with the kind assistance of that able chemist
and microscopist, Mr. Henry Deane, of Clapham Common, I obtained,
by immersing chalk in dilute hydrochloric acid, and mounting the
residue in Canada balsam, several specimens of the entire integuments
of the bodies of Rotaliæ, as distinct as if recent! This fact is
now admitted; and the experiment has been successfully repeated in
India, by Mr. Carter, on the limestones of that country;[120] and in
America, by Dr. Bailey, &c.[121] In some limestone recently collected
by my eldest son, Mr. Walter Mantell, in the Middle Island of New
Zealand, and which, like our cretaceous strata, is almost entirely
made up of foraminifera, I have detected the soft parts of the bodies
of Rotaliæ in the cells of the fossil shells, as distinctly as in the
chalk of England; and two of the species appear to be identical with
European forms.
[Footnote 118: These "Notes" were withdrawn, and published in the
Annals of Natural History for August, 1845.]
[Footnote 119: Published in Philos. Trans. Part iv. for 1846.]
[Footnote 120: "On the existence of Beds of Foraminifera, recent and
fossil, on the South-East of Arabia," by H. J. Carter, Esq. Assistant
Surgeon, Bombay. Proceedings of the Bombay Asiatic Society, 1848.]
[Footnote 121: A remarkable foraminiferous deposit of chalk detritus
occurs at Charing, in Kent, and was first examined and described
by William Harris, Esq.; it contains immense numbers of many kinds
of foraminifera, and of the cases or shells of entomostraca, of
the genus Cytherina, with spicules of sponges, &c.--See Wonders of
Geology, vol. 1. p. 324.]
M. D'Orbigny gives the following summary of the distribution of the
known fossil species of Foraminifera:--
There are 228 species in the Tertiary deposits of Vienna alone, of
which twenty-seven species are known living in the Adriatic and the
Mediterranean.
Foraminifera are unknown in the Silurian and Devonian formations.
One species only is known in the Carboniferous system of Russia, the
_Fusulina cylindrica_.
Jurassic or Oolitic formation Genera 5 Species 20
Cretaceous " 34 " 280
Tertiary " 56 " 450
Living in the present seas " 68 " 1,000
Of these last, 575 species inhabit tropical seas, 350 the seas of
temperate, and 75 the seas of cold climates.
XIII. Fossil Elk of Ireland, or _Cervus megaloceros_. (Plate
LXXI.)--The shell-marls of Ireland contain in abundance the bones of
an animal, which like the Dodo, was once contemporary with the human
species, but has long been extinct: the last individuals of the race
were, in all probability, exterminated by the early Celtic tribes.
The remains of this noble creature generally occur in the deposits of
marl that underlie the peat-bogs, which are apparently, like those
of Scotland, the sites of ancient lakes or bays. In Curragh immense
quantities of these bones lie within a small area; the skeletons
appear to be entire, and are found with the skull elevated, and the
antlers thrown back on the shoulders, as if a small herd of these
Elks had sought refuge in the marshes, and had been engulfed in
the morass, in the same manner as the Mastodons of America. (See
description of Plate LXXIV., ante, p. 167.)
This creature far exceeded in magnitude any living species of elk
or deer. The skeleton is upwards often feet in height to the top of
the skull, and the antlers are from ten to fourteen feet from one
extremity to the other. The fine perfect skeletons in the British
Museum, College of Surgeons, and in the Museum at Edinburgh, render
a particular description unnecessary. The bones are generally well
preserved, of a dark brown colour, with patches of blue phosphate
of iron. In some instances they are in so fresh a condition, that
the hollows of the long bones contain marrow having the appearance
of fresh suet. Remains of this majestic animal have been found
collocated with ancient sepulchral urns, stone implements, and rude
canoes, in such manner, as to leave no doubt that this now extinct
deer was coeval with the early human inhabitants of these Islands.
Its bones and antlers have been found at Walton, in Essex, associated
with the remains of the Mammoth, or fossil elephant.[122]
[Footnote 122: Wonders of Geology, p. 134.]
XIV. Fossil Infusoria--_Infusorial Earths_.--In the note on
Foraminifera some account is given of various rocks composed of the
fossil remains of those minute animals; but the durable relics of the
yet more infinitesimal organisms designated by the terms _Infusoria_,
or _Infusorial animalcules_, form deposits of equal interest and
importance. Strata of great extent and thickness are wholly, or
in great part, made up of innumerable layers, consisting of the
aggregated siliceous cases or shields of Infusoria: and similar
structures are found to be the chief constituents of the white earthy
deposits of lakes, rivers, and basins of brackish water, in every
part of the world.
Slowly, imperceptibly, but incessantly, are the vital energies of
the feeblest and minutest animal and vegetable existences separating
from the element in which they live, the most enduring of mineral
substances, silex--fabricating it into structures of the most
exquisite forms and sculpturing, and thus adding to the accumulations
of countless ages, which make up the sedimentary strata of the crust
of the globe.
In the "Medals of Creation"[123] will be found a summary of what
was then known as to the formation and composition of many tertiary
deposits which the indefatigable Ehrenberg, Dr. Bailey, and other
eminent observers, had carefully investigated and described. The
five years that have since elapsed have been fruitful in results of
the most important and interesting character; from every quarter of
the world, from the loftiest mountain peaks, and from the deepest
recesses of the ocean which the plummet can reach, from the ashes of
volcanoes and from the snow of the glaciers, the durable remains of
Infusoria have been obtained. That excellent scientific periodical,
Silliman's American Journal, contains numerous interesting
communications on this subject from the eminent chemical professor
of the Military College at West Point, Dr. J. W. Bailey; and the
labours of Mr. Bowerbank, Williamson, and other active members of
the Microscopical Society of London, have yielded much interesting
information on the infusorial deposits of our own country.
[Footnote 123: Medals of Creation, vol. i. p. 211.]
The present note will be restricted to remarks on the nature of the
organisms which enter so largely into the composition of certain
tertiary deposits; since the opinion once entertained of the
animal nature of many infusoria, now regarded as true vegetables,
materially affects the geological conclusions respecting the
persistence of certain species of organisms through long periods of
time, during which the mollusca, zoophytes, &c. underwent repeated
mutations both in the species and genera. Thus, for example, the
_polierschiefer_, or polishing-slate of Bilin, and the berghmehl
of Tuscany, are described by Ehrenberg as masses of the siliceous
shells of animalcules of such extreme minuteness, that a cubic inch
of the stone contains upwards of forty millions; the infusorial
earth of Richmond, in Virginia, in like manner, is stated to be
made up of the siliceous skeletons of animalcules of infinitesimal
minuteness. But later investigations have (I conceive) satisfactorily
established, that the greater part of these fossil organisms belongs
to the vegetable and not to the animal kingdom.[124] The whole of the
figures in Plate IV. of the "Medals of Creation," described as living
Infusoria, on the authority of Ehrenberg, are undoubted vegetables,
belonging to the great botanical groups called _Diatomaceæ_ (from the
angular segments into which they separate by partial division), and
_Desmidiaceæ_.[125] The entire family of _Bacillaria_ belongs to this
group. These simplest forms of vegetable structures abound in every
lake or stream of fresh and brackish water, in every pool, or bay,
and throughout the ocean, from the equator to the poles; they secrete
siliceous envelopes, which present an endless variety of form and
structure, and after the death and decomposition of the perishable
tissues of the plants, remain as perfectly transparent colourless
shields of pure silica; such are the _Gaillonellæ_, _Euastra_,
_Closteria_, _Naviculæ_, _Synhedræ_, _Podospheniæ_, _Xanthidia_,
&c., which constitute so large a proportion of the infusorial earths
described by Ehrenberg and other authors.[126]
[Footnote 124: In my little work on Recent Infusoria, entitled
"Thoughts on Animalcules, or a Glimpse of the Invisible World
revealed by the Microscope," I have expressed my conviction of
the vegetable nature of these organisms, as a reason for omitting
figures and descriptions of any of the species in a work on living
fresh-water animalcules.]
[Footnote 125: The name Diatomaceæ is restricted by M. Brébisson to
those species which have a siliceous envelope, or cuticle; and that
of _Desmidiæ_ to those which are not siliceous, but reducible by heat
to carbon.]
[Footnote 126: The reader interested in this subject should consult
the beautiful work of Mr. Hassall on the Desmidiaceæ, published by
Messrs. Reeve & Benham.]
The extent of this infinitesimal flora throughout regions where no
other forms of vegetation are known, is strikingly demonstrated by
the observations of the eminent botanist and traveller. Dr. Hooker,
in his account of the Antarctic regions.
"Everywhere," he states, "the waters and the ice alike abound in
these microscopic vegetables. Though too small to be visible to the
unassisted eye, their aggregated masses stained the iceberg and
pack-ice wherever they were washed by the sea, and imparted a pale
ochreous colour to the ice. From the south of the belt of ice which
encircles the globe, to the highest latitudes reached by man, this
vegetation is everywhere conspicuous, from the contrast between its
colour and that of the white snow and ice in which it is imbedded. In
the eightieth degree of south latitude all the surface ice carried
along by currents, and the sides of every berg, and the base of the
great Victoria barrier itself--a perpendicular wall of ice, from one
to two hundred feet above the sea-level--were tinged brown from this
cause, as if the waters were charged with oxide of iron. The majority
of these plants consist of simple vegetable cells, enclosed in
indestructible silex (as other _Algæ_ are in carbonate of lime); and
it is obvious that the death of such multitudes must form sedimentary
deposits of immense extent.
"The universal existence of such an invisible vegetation as that of
the Antarctic ocean, is u truly wonderful fact, and the more so,
from its being unaccompanied by plants of a high order. This ocean
swarms with mollusca, and entomostracous crustaceans, small whales,
and porpoises; and the sea with penguins and seals, and the air with
birds: the animal kingdom is everywhere present, the larger creatures
preying on the smaller, and these again on those more minute; all
living nature seems to be carnivorous. This microscopic vegetation is
the sole nutrition of the herbivorous animals; and it may likewise
serve to purify the atmosphere, and thus execute in the antarctic
latitudes the office of the trees and grasses of the temperate
regions, and the broad foliage of the palms of the tropics."[127]
[Footnote 127: From Dr. Hooker's account of the botany of the South
Polar regions in Sir J. Ross's Voyages of Discovery.]
Dr. Hooker also observes, that the siliceous cases of the same kind
of Diatomaceæ now living in the waters of the South Polar Ocean,
have contributed in past ages to the formation of European strata;
for the tripoli and the phonolite stones of the Rhine contain the
siliceous shields of identical species. Such are the comments of one
of our most eminent botanists on the phenomena under review. The
reader will probably ask,--What, then, are the essential characters
which separate the animal from the vegetable kingdom? To this
question it is impossible to give a satisfactory reply: perhaps the
only distinction that will be generally admitted by zoologists and
botanists is the following:--_animals require organic substances for
their support; vegetables derive their sustenance from inorganic
matter_.
The facts thus cursorily reviewed throw much doubt on many of M.
Ehrenberg's statements as to the identity of species of animalcules
now living, with those whose remains occur in the eocene, and in
the secondary strata. The so-called _Xanthidia_ of the chalk, are
certainly altogether distinct from the recent diatomæ to which the
name was first applied; the chalk organisms are probably the gemmules
of sponges or other zoophytes.[128]
[Footnote 128: It would be convenient to distinguish these fossils by
another name, and thus avoid the perpetuation of the error; I would
propose that of _Spiniferites_, in allusion to the numerous spines
with which all the species are beset.]
Infusorial earths may therefore be composed either of microscopic
vegetable or animal remains, or of both. The brackish and
fresh-water deposits I have examined are siliceous and almost wholly
diatomaceous: the marine calcareous strata composed of microscopic
organisms, consist chiefly of various kinds of foraminifera, a large
proportion belonging to the polythalamia, or chambered shells. I
am not certain as to the animal or vegetable nature of some of
the beautiful siliceous disks (_Coscinodisci_, _Arachnoidisci_,
_Actinocyclus_, &c.) so abundant in the Richmond, Barbadoes, and
Bermuda infusorial earths, and which occur in so splendid a state in
the Guano deposits of Ichaboe.
With the corrections which the above remarks will enable the reader
to make, I would refer to the account of Fossil Infusoria in the
Medals of Creation, and Wonders of Geology. [129]
[Footnote 129: See also "Thoughts on Animalcules."]