FOSSIL FORAMINIFERA--MICROSCOPICAL EXAMINATION OF CHALK AND FLINT.
"Where is the dust that has not been alive?"
Young.
That those infinitesimal forms of animal existence which swarm
throughout the waters of the ocean, but whose presence can only be
made manifest by the aid of the microscope, are preserved in a fossil
state,--that their durable remains constitute mountain ranges, and
form the subsoil of extensive regions,--and that the most stupendous
monuments erected by man are constructed of the petrified relics of
beings invisible to the unassisted eye,--are facts not the least
astounding of those which modern Geology has revealed.
This interesting field of research, which the labours of that eminent
observer M. Ehrenberg first made known, has since been explored
by other naturalists, and in every part of the world many of the
Tertiary and Secondary deposits have been found to contain microscopic
organisms in profusion. At present this branch of palæontology is in
its infancy, and it offers to the young student an inexhaustible and
most attractive path of scientific investigation; it possesses, too,
this great advantage over many others, that it can be pursued at home,
and the materials for its prosecution are everywhere at hand. Unlike
my explorations in the Wealden, in which a few fragments of bones, or
teeth, scattered at wide intervals through the rocks, and in localities
many miles apart, were often the only reward of a day's labour, here,
in the quiet of my study, I may discover in a few atoms of flint,
or grains of chalk, picked up by the road-side, the fossil remains
of beings as interesting and extraordinary as the extinct colossal
reptiles of Tilgate Forest.
[Sidenote: MICROPHYTES.]
The microphytes, or fossil Diatomaceæ, described in a previous chapter,
(_ante_, p. 93,) were formerly classed with the organisms that now
claim our attention, under the name _Infusoria_; from the belief that
generally prevailed among naturalists, of their animal origin. In fact,
some eminent microscopic observers, while admitting the vegetable
character of Xanthidium, Micrasterias, &c. consider the Naviculæ,
Ennotiæ, &c. as belonging to the animal kingdom.
Thus Dr. J, W. Bailey, in a late "Memoir on the Microscopic Organisms
in Various Localities of the United States," divides these bodies into
three groups; viz. _Infusoria_, _Desmidieæ_, and _Diatomaceæ_; with the
remark, that he has separated the two latter tribes from the Infusoria,
because so many distinguished naturalists consider them decidedly to
belong to the vegetable kingdom: "but," he adds, "while I believe that
no positive line of separation can be drawn between certain animals and
vegetables, I am yet disposed to regard the _Desmidieæ_, from the sum
of all their characters, as most nearly allied to admitted vegetables;
while the _Diatomaceæ_, notwithstanding Mr. Thwaites's interesting
observations on their conjunction,[305] still seem to me, as they have
always done, to be true animals. There is such apparent volition in
their movements, such an abundance of nitrogen in the composition
of their soft parts, and such resemblance between the stipitate
Gomphonematæ and some of the Vorticellæ, that I should be still
disposed to class them as animals, even if Ehrenberg's observations
of the retractile threads and snail-like feet of some of the Naviculæ
should not be confirmed."[306]
[305] The mode of fructification, or _conjunction_, as it is termed,
in the Algæ, consists in the adhesion of two cells or frustules
together, and their fusion into one; from their united contents a
mass of granular substance is produced, that becomes consolidated and
forms the spore or fruit, which, when arrived at maturity, is set free
by the bursting of the cell. Mr. Thwaites has ascertained that the
fructification is similar in the Diatomaceæ.
[306] Smithsonian Contributions, vol. ii. p. 34.
Thus, whilst referring Closterium, Arthrodesma, Euastrum, Xanthidium,
Micrasterium, &c. as vegetables, to the Desmidieæ, Dr. Bailey
places, _Actinocyclus_, _Campilodiscus_, _Coscinodiscus_, _Ennotia_,
_Navicula_, _Gomphonema_, _Pinnularia_, _Triceratium_, &c. among the
Diatomaceæ, as animals.
Of the animal nature of the microscopic objects which now require
our attention, there is however no question, although the zoological
position and affinities of many of the organisms included in this
survey are still but imperfectly determined.
The animals designated _Foraminifera_,[307] or Rhizopoda,[308] are of a
more simple structure than the Polypifera and Echinodermata described
in the previous chapters; yet as their relics are for the most part
presented to the notice of the geologist as aggregations of shells,
forming extensive beds of limestone, it will be convenient to treat of
them in this place.
[307] Foraminifera, _i.e._ bearing foramina--a name derived from the
minute openings in the shells and their septa.
[308] Rhizopoda; root-like feet; from the long fibrous processes, or
pseudopodia.
The fact that the fossil remains of Foraminifera, and of _Mollusca_,
alike consist of shells, and constitute strata identical in mineral
characters, and deposited under like physical conditions, renders the
examination of these Microzoa[309] a fit introduction to the study of
the durable remains of the higher order--the Mollusca.
[309] Microzoa; from μικρος, _mikros_, small, and ζωον, _zoon_, animal;
a convenient term to denote minute animal organisms whose forms can
only be defined by the aid of the microscope.
It is scarcely more than a hundred and twenty years ago, that the
existence of this numerous order of microzoa was first made known to
naturalists by _Beccarius_, who detected a considerable number of
species in the sand on the shores of the Adriatic. But the structure of
the animals that secreted these shells is a discovery of comparatively
modern date. The early collectors classed these microscopic bodies with
the shells of true mollusca; and even M. D'Orbigny, whose elaborate
researches justly constitute him a high authority in this branch of
natural history, in his first memoir, in 1825, described the involuted
discoidal forms as Cephalopoda. This error was corrected by the
investigations of M. Dujardin, who in 1835 satisfactorily demonstrated
that the Foraminifera are animals of the most simple structure, and
entirely separated by their organization from the Mollusca.
But the true nature of this class is so little understood by British
collectors of fossil shells,--of course I mean the uninitiated, and
the amateur naturalist, for whose use these unpretending pages are
designed,--that in order to invest the study of the fossil species with
the interest which a knowledge of the structure and economy of the
living originals can alone impart, I must give a history of the recent
forms somewhat in detail, taking M. D'Orbigny as my chief authority.[310]
[310] The best work for the student to consult is M. D'Orbigny's
"Foraminifères Fossiles du Basse Tertiaire de Vienne, Autriche." Paris,
1846. 1 vol. 4to. with plates. I rejoice to learn that a Monograph
on the British Foraminifera is in preparation by Dr. Carpenter and
Professor Williamson: than whom there are none more competent.
[Sidenote: FORAMINIFERA.]
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 in a spiral, or involuted round an axis.
This body is covered with an envelope or shell, which is generally
testaceous, rarely cartilaginous, 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 the 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, ochreous, 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. The animal increases by gemmation, each segment being
essentially distinct, but connected with the preceding one by a tube or
neck. 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.
The segments, which successively appear, are agglomerated together
in seven different ways, and these modifications are the basis of M.
D'Orbigny's classification. The discoidal forms, as the _Rotalia_,
_Rosalina_, _Cristellaria_, &c. are involute, like the Nautilus, and
divided by septa or partitions, which, like the enveloping shell, are
perforated. The lobes of the body _occupy contemporaneously every
chamber_, and are connected by a tube that extends through the entire
series. In the spiral form, as the Textularia, &c., the same structure
is apparent.
Whatever the form of the body, the filaments always consist of a
colourless transparent matter; they are capable of being elongated to
six times the diameter of the shell. They often divide and subdivide,
so as to appear branched; and though alike in form in the different
genera, vary much in their position. In some species they form a bundle
which issues from a single aperture, and is withdrawn into the same by
contraction; in others, the filaments project only through each of the
pores in that portion of the shell which covers the last segment: in
many they issue from both the large aperture and the foramina. These
filaments or pseudopodia fulfil in these animals the functions of
the numerous tentacula in the Star-fishes; serving as instruments of
locomotion and attachment.
Neither organs of nutriment nor of reproduction have been discovered.
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; though less
complicated than the Echinoderms and the Polypifera in their internal
organization, they have the mode of locomotion of the first; while by
their free, individual existence, they are more advanced in the scale
of being than the aggregated and immovably fixed animals of the latter
class.
But though I consider the animal of the Foraminifera as single, and
the additional lobes, or segments, as the continuous growth of the
same individual, I must state that some eminent naturalists regard
the entire structure as a series of distinct individuals, developed
by gemmation from the first formed segment, like the clusters of
the compound _Tunicata_; and not as a single aggregated organism,
made up of an assemblage of similar parts indefinitely repeated. In
a palæontological point of view, it matters not which opinion is
adopted.[311]
[311] See a masterly paper on the structure of Nummulina and Orbitoides,
by Dr. Carpenter; Geol. Journal, vol. vi. pp. 21-39, with admirable
representations of the structural details.
[Illustration: Lign. 109. Foraminifera.
_Chalk. Charing._
Fig. 1.--Globigerina cretacea; the original is 1/60 of an inch in
diameter.
2.--Textularia Globulosa; 1/40.
3.--Verneuilina tricarinata; 1/30.
4.--Cristellaria rotulata; 1/40.
5.--Rosalina Lorneiana; 1/40.
]
[Sidenote: CLASSIFICATION OF THE FORAMINIFERA.]
Classification of the Foraminifera.--The number of genera is so great,
that I can only attempt to convey a very general idea of the principles
of classification adopted by M. D'Orbigny, and give a few illustrations
of some of the most abundant fossil species.
That the reader may be cognizant of the usual aspect of these shells
five specimens from the Chalk, belonging to as many genera, are here
represented (_Lign. 109_); the deposit whence they were obtained will
be described hereafter.
As the mode in which the growth of the body, and consequently of the
shell, takes place, differs greatly in certain groups, an obvious and
natural arrangement is suggested, by which the class is divided into
seven orders:--
1. The primary, or simplest type; one segment or cell; as in _Orbulina_.
2. The segments arranged in circular lines; as in _Orbitolina_.
3. Segments disposed in a straight or arched single line; successively
increasing from the first to the last cell; as in _Nodosaria_, _Lign.
111_.
4. Segments, spirally and discoidally disposed, on the same plane, like
cells of the Nautilus; as in _Cristellaria_, _Lign. 109_.
The same type, but coiled obliquely, and inequilaterally, like the
shells of Gasteropoda; as in _Globigerina_, _Lign. 109_, _Rosalina_,
_Lign. 109_.
5. Segments developed alternately on the right and left of the
first, and successively on each side the longitudinal axis; as in
_Textularia_, _Lign. 109_.
6. Arrangement of the segments combining the modes of 4 and 5; that is,
the segments are formed alternately, but the whole are coiled spirally,
either obliquely, or on the same plane; as in _Amphistigena_.
7. Segments round a common axis, on two, three, four, or five, opposite
faces, returning after each entire revolution; the new cells being
placed exactly on the preceding series; as in _Quinqueloculina_, _Pict.
Atlas_, pl. lxii. _fig._ 12.
The Foraminifera vary considerably in magnitude; by far the greater
number of species are invisible to the unassisted eye, and the aid
of a lens or microscope is required to define the structure even of
the largest; yet many are of sufficient size to be recognized, as for
example the _Spirolinæ_, _Lign. 112_. A few genera are from a quarter
of an inch to nearly an inch in diameter, as the _Orbitoides Mantelli_
of the tertiary formations of North America,[312] and the _Nummulina_,
commonly termed _Nummulites_, of Europe, _Lign. 110_.
We will now describe the genera selected for illustration,
commencing with the large and well-known type, whose aggregated
remains form extensive beds of crystalline limestone in the Alps,
and in Asia, and Africa.[313]
[312] Dr. Morton's Synopsis of the Organic Remains of the Cretaceous
group of the United States. Philadelphia, 1824, p. 45, pl. v. fig. 9.
[313] Geol. Journal, vol. v.
[Illustration: Lign. 110. Nummulites, or Nummulina; _nat._
_From the Great Pyramid of Egypt._
Fig. 1.--Transverse section of a Nummulite, showing the form and
arrangement of the cells.
2, 3.--Specimens with part of the external plate removed.
]
Nummulina lævigata. _Lign. 110._--The shell is of a discoidal or
lenticular form, composed of numerous cells, concentrically arranged
round an axis on the same plane; both sides of the disk covered by a
smooth thick plate.
[Sidenote: NUMMULITES.]
Under the name of _Nummulites_, from their resemblance to a piece of
money, the fossil shells of this genus of Foraminifera have long been
known to naturalists, and are figured in many of the early works on
petrifactions. They occur in immense quantities in certain rocks, and
are of all sizes, from a mere point, to disks an inch and a half in
diameter; thus exceeding in magnitude all other animals of this class.
Perfect specimens appear as a calcareous solid circular body, of a
lenticular shape; smooth, and slightly convex on both sides, and
without any visible structure. On splitting the fossil transversely,
or rubbing down one of the convex planes, a series of minute cells,
arranged in a discoidal spire, is brought to view, as shown in _Lign.
110, fig. 1_. But this description gives a very inadequate idea of the
complicated and exquisite structure of the original, which has been
admirably worked out by Dr. Carpenter. This eminent physiologist has
shown that each chamber was occupied by a living segment, connected
with other segments by one or more tubular prolongations, which
absorbed nutrition from without, by means of filamentous pseudopodia,
that projected through a system of passages leading from the medial
plane to the external surface.[314] A figure of the supposed form of a
living Nummulina is given in Pict. Atlas, p. 187.
[314] Geol. Journal, vol. vi. p. 21. See also a paper by Prof.
Williamson, "On the minute Structure of the Calcareous Shells of some
recent species of Foraminifera." Trans. Microscop. Soc. vol. iii. p.
105.
The specimens figured in _Lign. 110_ are from the limestone that
forms the foundation rock of the Great Pyramid of Egypt, and of which
that structure is in great part composed. Strabo alludes to the
Nummulites of the Pyramids, as lentils which had been scattered about
by the artificers employed on those stupendous monuments, and become
stone.[315] Silicified masses of Nummulites are occasionally met with;
polished slices of such specimens are richly figured by the sections of
the inclosed Foraminifera.
[315] An interesting fact was communicated to me by a friend who
lately descended the Nile; the Nummulitic limestone rocks are in some
parts of the course of the river washed into the stream, and becoming
disintegrated, the Nummulites are set free, and re-deposited in the
recent mud of the Nile.
The Nummulitic limestones are of the Eocene or ancient. Tertiary epoch,
as the labours of Sir Roderick Murchison in the Alps, Apennines, and
Carpathians first established: Nummulites are unknown in the Secondary
formations.[316]
[316] Geol. Journal, vol. v.
Orbitoides.--The fossil bodies thus named are disciform, like the
Nummulites; and one species, which forms the constituent substance
of ranges of limestone mountains, 300 feet high, near Suggsville, in
North America, was first described by my lamented friend, the late
Dr. Morton, of Philadelphia, as _N. Mantelli_, in his work on the
Cretaceous Fossils of the United States.
The discovery that the Nummulitic deposits of the Old World were of
the tertiary period, directed attention to their supposed geological
equivalents in America; and on a careful examination of their fossils,
the rocks proved to be tertiary, and the shells true Foraminifera
allied to the Nummulites, but generically distinct.[317] A reference to
Dr. Carpenters memoir, previously cited, is necessary to comprehend the
complicated structure of these fossils.[318]
[317] Manual of Geology, p. 208.
[318] Geol. Journal, vol. vi.
Siderolina, or _Siderolites_, is a genus of Foraminifera, which may
be described as Nummulites, in which the turns of the spire are
intercepted by elongated appendages, that project beyond the periphery
of the disk, and produce a stellated figure. These fossils abound in
the cretaceous strata of Maestricht.
Fusulina.--The shell is fusiform, being elongated transversely to
the axis; the cells are divided internally by constrictions. Only
one species is known, (_F. cylindrica_,) and this is confined to the
Carboniferous formation; it is the most ancient or earliest type of the
class, according to the present state of our knowledge.
[Illustration: Lign. 111. Foraminifera, &c.
Fig. 1 and 2.--Campilodiscus; a perfect frustule, and part of another,
seen from above, Tertiary; Egra in Bohemia. _See ante_, p. 96.
3_a_.--Lituola nautilotdea. _Chalk, Chichester._ (By Mr. Walter
Mantell.) Side view, × 8.
3_b_.--Front view of the last cell of 3d, to show the foramina with
which it is pierced.
3_c_.--The last cell of 3_a_.
3_d_.--Side view of a young shell, before the produced, or straight
part appears, × 20.
4_a_.--Flabellina Baudonina. _Chalk._ (M. D'Orbigny.) A young
individual seen in profile, × 12.
4_b_.--The same, viewed laterally, shows the oblique arrangement
of the cells.
5.--Nodosaria. _Chalk, Chichester._ (By Mr. Walter Mantell.) The
line below indicates the natural size.
]
[Sidenote: NODOSARIA. LITUOLA.]
Nodosaria. _Lign. 111, fig. 5._--Straight, elongated cells placed
end to end, separated by constrictions; the last formed cell has a
round central aperture. Several beautiful species abound in the Chalk;
specimens often occur adhering to the surface of the flint nodules.
Nodosariæ are abundant in tertiary deposits. Mr. Walter Mantell
discovered Foraminifera of this genus in the blue clay of Kakaunui, in
New Zealand.
Cristellaria. _Lign. 109, fig. 4._--The shell is in the form of a
compressed Nautilus; it has a single aperture, which is situated at the
angle of the keel; the cells are oblique.
This genus comprises seventy fossil species, which occur in the Lias,
Oolite, and Chalk. Living species are abundant in almost every sea.
Flabellina. _Lign. 111, fig. 4a_.--In a young state, this shell,
like the preceding, resembles that of a Nautilus, and the cells are
oblique; but in the adult, are of a zigzag (chevron) form. It has a
single round aperture. _Fig. 4a_ shows a young individual, seen in
profile; _fig. 4b_ a lateral view, exhibiting the obliquity of the
cells.
Species of Flabellina are often found in cretaceous strata. The genus
is not known in a recent state.
Polystomella.--In its general form this genus resembles the other
nautiloid shells above described, but its structure differs
essentially; for there are several apertures along the side of the
shell, as well as the opening in the last segment. The cells are
simple, and each is a single cavity. The figures and details of
structure, given by Professor Williamson, must be referred to, for an
insight into the organization of this beautiful and complicated type
of Foraminifera.[319] One species of Polystomella is said to occur in
the Chalk; I have not detected this genus in our cretaceous deposits.
Recent species swarm in our seas; and may be easily obtained from the
mud and sand on the shores at Brighton.[320]
[319] Trans. Microscop. Society, vol. ii.
[320] Mr. Poulton has specimens of the shells, and the bodies of the
animals deprived of the shell, mounted for the microscope.
Lituola. _Lign. 111, fig. 3a._--In a young state the shell is
nautiloid, as in _fig. 3b, 3d_; but becomes produced by age, and
assumes a crosier-like form, as in _fig. 3a_. The cells are filled
with a porous testaceous tissue, as shown in _figs. 3b, 3c_; which
also illustrate the foraminiferous character of the shells in this
class of animals; for both the external testaceous covering, and the
septa of the cells, exhibit perforations.[321]
[321] The perforations are omitted, by mistake, in the figure of the
adult shell, _fig. 3a_.
[Illustration: Lign. 112. Spirolinites in Flint.
_Chalk. Sussex._
(_By the late Marquis of Northampton._)
The specimens are only sections of the shells Imbedded in flint, and
seen as opaque objects with a lens of moderate power. The small figures
denote the size of the originals.]
[Sidenote: SPIROLINA.]
Spirolina. _Lign. 112._--The general form resembles that of Lituola:
the young shell being a discoidal, involute, and becoming produced
by age; but the internal structure is different; the cells are simple
cavities.
The chalk and flints of Sussex abound in these crosier-like shells,
whose existence in the cretaceous rocks was first made known by my
deeply lamented friend, the late Marquis of Northampton. The annexed
lignograph, from drawings by his lordship, shows the form and structure
as displayed by sections in fractured flints. Four species were named
by Lord Northampton (see _Wond._ p. 32-5); but it is doubtful whether
all the specimens belong to more than one species; the apparent
diversity of structure may arise simply from the different planes in
which the sections happen to have been made.
Globigerina. _Lign. 109, fig. 1._--The shell is turbinated, the cells
are spheroidal, and the last, or terminal one, has a semilunar aperture
at the umbilical angle. Several fossil species abound in the Chalk and
in the tertiary deposits; and many living species swarm in our seas.
[Illustration: Lign. 113. Nonionina Germanica, × 290.
A recent specimen of the body of the animal; the shell removed by acids.
_From the North Sea, Cuxhaven._ (_M. Ehrenberg._)
_a, a._--Naviculæ and other organisms in the segments of the animal.]
Nonionina.--_Lign. 113._--A nautiloid shell, with simple cells; the
last cell has a single narrow aperture placed transversely over the
dorsal aspect of the spire. One species occurs in the chalk formation
of Germany; several in tertiary deposits, and in the existing seas.
The figure, _Lign. 113_, represents the body of the animal deprived of
its shell, to illustrate the nature of certain fossils from the Chalk.
[Illustration: Lign. 114. Foraminifera in Chalk and Flint. × ×.
(_Seen by transmitted light._)
Figs. 1, 2, 3, 6.--Different forms of Rotalia.
2.--Resembles the recent Rotalia stigma; Ehrenberg;
from the North Sea, near Cuxhaven.
4.--Portion of a Nautilus, showing five chambers, partially
separated, each pierced by the siphunculus: in Flint, from
Ireland.
5.--The body of a Rotalia, in Flint; the shell is not
apparent.
]
[Sidenote: ROTALIA--ROSALINA.]
Rotalia. _Lign. 114._--The shell, though nautiloid in its contour,
is regularly turbinated, the cells not globular; the last cell has
a central, semilunar, transverse, aperture. There are fifty fossil
species. The Rotaliæ appear in the Lias, Oolite, and Chalk, in immense
numbers, and swarm in the present seas.
Rosalina. _Lign. 109, fig. 5._--The shell is depressed; the spire
apparent on one side; the aperture is a prolonged slit extending from
one cell to another, and opening on the umbilicus; that is, on the
side opposite to the spire. There are eighteen fossil, and many recent
species of this genus.
Textularia. _Lign. 109._--This, and the following genus, belong to
that order of Foraminifera in which the segments or cells are arranged
in two or three distinct axes (_ante_, p. 342), and by their gradual
increase give rise to an elongated conical but not spiral shell, which
in its general outline resembles that of certain gasteropoda, but is
easily distinguished by its internal structure. The shell is conical,
compressed, formed of alternate cells, with a transverse aperture
placed on the inner side. Upwards of thirty fossil species are known.
The Textulariæ are in great abundance in the cretaceous rocks; and,
together with Rotaliæ and Rosalinæ, constitute a large proportion of
the minute organisms of the secondary formations as well as of the
present seas.
Verneuilina.--_Lign. 109, fig. 3._--A turriculated shell, with a slit
or aperture transverse to the axis of involution, and placed on the
umbilicus. This genus, of which but one species is known, is peculiar
to the cretaceous deposits.
* * * * *
[Sidenote: CHALK ANIMALCULITES.]
Strata composed of Foraminifera.--From this concise exposition of
the characters of the genera that most frequently occur in a fossil
state, we pass to the examination of the organic composition of those
limestones which are in a great measure made up of the debris of
Foraminiferæ. We will commence the investigation with that common
substance, the white chalk of the South-East of England.
It has long been known that a large proportion of the purest white
chalk consists of minute chambered shells,[322] and corals.
[322] Often termed _Polythalamia_, meaning many chambers or cells.
Mr. Lonsdale, some years since, first showed that by brushing chalk in
water, and examining the sediment, shells, corals, and foraminifera
might be obtained in abundance; but it was not at that time suspected
that the residue of the detritus was almost entirely composed of
distinct organic structures, so minute as to require high magnifying
powers, and a peculiar mode of manipulation, for their detection and
definition.
M. Ehrenberg demonstrated that even the fossils discovered by Mr.
Lonsdale are colossal, in comparison with the infinitesimal structures
of which the finer particles of the chalk consist; for one cubic
inch of the limestone is found to contain upwards of a million of
well-preserved animal organisms.
The chalk, therefore, is an aggregation of extremely minute fossils
and inorganic particles. The yellow, soft, writing chalk of the North
of Europe, according to M. Ehrenberg, is composed of about half its
mass of organic remains; but in the chalk of the South of Europe, the
fossils predominate. The amorphous atoms of the cretaceous limestone
do not, as was formerly believed, arise from a precipitate of lime
previously held in solution, but from the disintegration of the
assembled organisms into more minute calcareous particles; and these
have subsequently been reunited by a crystalline action, into regular,
elliptical, granular, bodies.
M. Ehrenberg infers that the compact flint nodules have originated from
an aggregation of pulverulent particles of siliceous organisms; and
upon this hypothesis explains the absence of flint nodules, and the
abundance of siliceous infusoria, in the beds of marl that alternate
with the chalk in the south of Europe, and their presence in the chalk
of northern Europe, in which the marls are wanting. In other words,
he supposes, that in the former case the siliceous shells of the
animalcules were spread abroad and deposited in layers or strata; and
in the latter were aggregated into nodular masses. This opinion is not,
however, supported by facts; for, though the animal origin of lime,
flint, and iron, may be admitted to a great extent, yet the deposition
of silex and lime from aqueous solutions, is carried on at the present
moment upon an enormous scale; and it cannot be doubted that to such a
process is attributable the formation of the nodules, layers, dikes,
and veins of flint, which traverse the chalk, and other rocks.[323]
[323] See my "Memoir on a Microscopical Examination of Chalk and Flint,"
Annals of Nat. Hist., Aug. 1845.
The most abundant microscopic organisms in the English chalk and flint
which I have examined, are _Rotaliæ_, or _Rosalinæ_, and _Textulariæ_.
Immense numbers of minuter Foraminifera also occur, and many shells,
which are unquestionably the young state of testaceous Cephalopoda (as
_Nautilus_, _Ammonite_, &c.).
Spines of Sponges, and of Echinoderms, also frequently appear in the
field of the microscope: and a spongeous structure is so common in
flint, that an eminent observer conceives that all the flints, both
nodular and tabular, have originated from poriferous zoophytes;[324] an
hypothesis altogether inadmissible.
[324] "Memoir on the Siliceous Bodies in the Chalk, Greensands, and
Oolite," by J. S. Bowerbank, Esq. F.R.S. &c. Geol. Trans, vol. vi. p.
181.
The assertion that the chalk every where consists almost wholly of
organic bodies must likewise be accepted with some limitation. The
assiduous observer who searches for hours chalk and flint carefully
prepared, and with the aid of an excellent microscope, though he
will meet with immense numbers of organisms, will often find a great
proportion of atoms without traces of structure. Neither is there
much variety in the easily recognizable forms of the English chalk (I
write from my own limited experience); many of the species described
by M. Ehrenberg, and others, are few and far between; and I have not
detected a single example of diatomaceæ. The student therefore must
not be discouraged, if, after perusing the glowing accounts of the
discoveries of M. Ehrenberg, he should not be more successful than
myself. It must, however, be borne in mind, that as the fossil remains
of the larger animals and plants are commonly associated together
in particular localities, while in similar rocks in other districts
they are altogether wanting; in like manner, some strata of the same
series may be made up of organic bodies, while others are destitute of
them. In fact, such is the case with our English Chalk: some layers in
the cliffs at Dover are literally an aggregation of foraminifera and
corals, while other beds have but few vestiges of organic remains.
[Sidenote: CHALK FORAMINIFERA.]
[Illustration: Lign. 115. Chalk-dust; chiefly composed of Foraminifera;
_highly magnified._
(_Seen by reflected light._)
_a, a._ Rotaliæ. _b._ Textulariæ.]
Foraminifera of the Chalk and Flint. _Lign. 115._--If a few grains
of soft white chalk from Gravesend or Dover be examined under a high
power (1/4 inch object-glass of Ross), groups of foraminifera will be
perceived, chiefly of Rotaliæ, Rosalinæ, and Textulariæ, as shown in
_Lign. 115_. If some of the powder be immersed in Canada balsam, (as
directed in the instructions at the close of this chapter for preparing
chalk for microscopical examination,) the outline of the shells, and
the cavities of, the cells, will be apparent; as in the sketches
_Lign. 114_, _ante_ p. 351. If a chip or slice of flint, rendered
transparent by immersion in oil of turpentine or Canada balsam, be
viewed first with a low power, (1 inch object-glass,) to discover a
good specimen, and afterwards under a high magnifier, (a 1/4 or an
1/8 object-glass,) the form of the shell and of the cells will be
distinctly seen, as in _Lign. 116_. In this beautiful fossil Rotalia,
the segments are as sharply defined as in a recent example: and one of
the cells (_a_) is seen to be lined with quartz crystals.
[Illustration: Lign. 116. Section of a Rotalia in flint.
(_Seen by transmitted light, and showing the chambers partially filled
with mineral matter._)
_a._ A cell lined with spar.
(× 250 _diameters_.)]
At first sight this fossil might be mistaken for a nautilus partially
filled with spar; but the reader will remark that the septa, or
partitions, have their convex surface towards the aperture; whereas
in the shells of the Cephalopoda (Nautilus, Ammonite, &c.) the septa
are concave anteriorly. In _Lign. 114_, _fig._ 4, a series of casts in
flint of the septa of a young Nautilus is represented; by comparing it
with the Rotaliæ in the same lignograph, _figs._ 2, 3, this distinction
will be obvious. And here it may be necessary again to point out the
essential character of the animal of the foraminifera, as distinguished
from that of the cephalopoda with chambered shells. In the latter,
the body of the mollusk only occupies the large outer chamber; the
internal compartments are empty dwellings, which the animal has
successively quitted in the progress of its growth, and with which
it has no connexion except by the siphunculus. In the Rotalia, and
allied forms, the body of the animal is inclosed within the shells, and
occupies every chamber contemporaneously at every stage: the cells are
always filled by the segments of the body. Hence when the shell, which
is calcareous, is dissolved in weak hydrochloric acid, the soft body
is exposed, and seen to extend to the innermost chamber. The segments
are connected by a membranous tube, which some naturalists regard as
a common channel of communication between the several digestive sacs
of which the body consists; for minute diatomaceæ which the animal has
swallowed, (according to Ehrenberg,) are seen within the membranous
sacs; as shown in _Lign. 113_, which represents the body of a
Nonionina, deprived of its shell. The importance of obtaining a correct
idea of this structure will presently appear.
When a recent Rotalia is immersed in dilute acid, the soft parts of
the body, deprived of the shell, may be obtained entire; they consist
of a series of little bags or sacs, united by a tube. The constituent
substance appears to be a tough membrane, and is generally of a rich
brown or amber colour. The sacs are sometimes full of a granular
substance, but are often empty and collapsed.
[Sidenote: FOSSIL BODIES OF ROTALIÆ.]
Fossil remains of the soft parts of Foraminifera. _Lign. 113._--When
examining chalk[325] and flint under the microscope with the view of
discovering the fossil bodies described by M. Ehrenberg, I observed
that the cells of the Rotaliæ in flint were frequently occupied by a
substance varying in colour from a light amber to a dark brown, and
closely resembling in appearance the body of the recent foraminifer
deprived of its shell. Under a high power, the folds of the membranous
sacs and the connecting tube were apparent, and I felt convinced that
the substance filling the cells was not inorganic, but the original
animal tissues in the state of molluskite.[326] In short, that the
animal had become immersed and preserved in the fluid silex like the
insects in amber. The appearance of the first discovered example of
this kind is represented in _Lign. 117_.
[325] In 1845.
[326] _Molluskite_: a name by which I proposed to distinguish the
carbonaceous substance resulting from the soft bodies of testaceous
mollusca.
[Illustration: Lign. 117. Rotalia in Flint, with the fossilized body of
the animal in the shell: _highly magnified_.
(_Seen by transmitted light._)]
[Sidenote: SOFT BODIES OF FORAMINIFERA.]
In a paper read before the Geological Society in 1845,[327] I
ventured to affirm the animal nature of the fossils in question; but
the supposition was regarded by geologists as very startling and
unsatisfactory; and as the specimens were enveloped in flint, the
appearance was attributed to the infiltration of mineral matter of a
different colour from the surrounding silex, into the empty chambers;
a circumstance of frequent occurrence in Ammonites, Nautili, and even
in the foraminifera; for the latter are often filled with chalk, flint,
silicate of iron, crystal, &c. as in _Lign. 116_. In these instances,
I conceive the shells were either empty when immersed in the fluid
chalk or flint, or speedily became so by the decomposition of the soft
parts of the animal. But in the fossils under consideration, I believe
the live animal was suddenly enveloped, and hermetically sealed, as
it were, in its shell, and that putrefaction was thus prevented.
The uniformity in colour, and the structure of the substance in the
cells, appeared to me incompatible with its assumed mineral origin,
and I resolved to follow up the inquiry by an examination of Rotaliæ
in chalk; in the hope that by dissolving the shell in acid (as in
recent foraminifera), the body of the animal might be detected in an
unmineralized state. After many fruitless attempts, several examples of
the soft bodies of Rotaliæ were obtained from the grey chalk of Dover,
in an extraordinary state of preservation.[328]
[327] Notes of a Microscopical Examination of the Chalk and Flint of the
South-East of England, with Remarks on the Animalculites of certain
Tertiary and Modern Deposits. Published in the Ann. Nat. Hist., Aug.
1845.
[328] To Henry Deane, Esq. of Clapham Common, I am indebted for some of
the most illustrative specimens hitherto obtained.
[Illustration: Lign. 118. The Soft Bodies of Foraminifera; extracted
from Chalk: _highly magnified_.
(_Viewed by transmitted light._)
Fig. 1.--An exquisite example of the body of a Rotalia; the sacs
partially collapsed.
2.--Body of a Rotalia; the sacs distended with a dark granular
substance.
]
These marvellous relics were obtained by subjecting a few grains
of the chalk to the action of weak hydrochloric acid, by which the
calcareous earth and the shells it contained were dissolved; the
residue, consisting of particles of quartz and green silicate of iron,
and remains of the animal tissues, were placed, in the usual manner, in
Canada balsam. Two exquisite specimens of the bodies of Rotaliæ thus
obtained are figured in _Lign. 118_.[329]
[329] I communicated this discovery to the Royal Society. See Philos.
Transactions, 1846, p. 465.
In these fossils the sacs are generally more or less distended with
a dark substance, as in _Lign. 118, fig. 2_: but in some, they are
empty and collapsed in folds, just as membranous pouches would appear
under similar conditions; as in the exquisite fossil, _Lign. 118,
fig. 1_.
The sacs regularly diminish in size from the innermost to the outermost
cell, and vary in number from fourteen to twenty-six; being more
numerous than in the recent species of Rotaliæ that have come under my
notice. In some instances small papillæ are seen on the outer surface
of the integument; apparently the vestiges of the pseudopodia.[330]
[330] Admirably as my excellent engraver, Mr. Lee, (of Prince's Square,
Kennington,) has executed the lignograph, 118, I would refer the reader
to the steel plate in Philos. Trans. 1846, pl. xxi. for figures of
these marvellous fossils.
Not only is the form and general character of the animal substance
preserved, but even its flexibility; for in one instance, the body,
released by the solution of the chalk and shell, was uncoiled and
pressed out, as shown in _Lign. 119, fig. 4_.
In one specimen, (figured in _Philos. Trans._ 1846, pl. xxi. _fig._
10,) the membrane of the largest sacs is much corrugated, and disposed
in numerous duplications, probably owing to the empty state of these
segments, when immersed in the chalk; but the discoidal contour of
the original is well preserved. This fossil so closely resembles the
decalcified body of a recent Rotalia or Rosalina, that an eminent
observer who saw it under the microscope at the meeting of the Royal
Society, without knowing its history, concluded it to be the body
of a recent animal. This extraordinary preservation of the soft
delicate tissues of an animal of the cretaceous seas, invisible to the
unassisted eye, through the incalculable ages that must have elapsed
since the deposition of the chalk in which it was enshrined, is a fact
as remarkable as the occurrence of the carcass of the Lena Mammoth, in
the frozen soil of Siberia.
[Sidenote: FORAMINIFERA IN CHALK AND FLINT.]
[Illustration: Lign. 119. Remains of Foraminifera; in Chalk and Flint.
(_Viewed by transmitted light; highly magnified._)
Fig. 1.--Shell of a Rosalina, filled with mineral matter; in flint.
2.--Soft parts of a Textularia; in flint.
3.--Cells of Textularia elongata; filled with mineral
matter; the shell not visible; in flint.
4.--The soft body of a Rotalia, deprived of its shell, and partially
uncoiled; obtained from Chalk, × 450 _diameters_.
]
The soft parts of other foraminifera have been discovered in a similar
state of preservation. A fine example of the body of a Textularia, in
flint, is figured, _Lign. 119, fig. 2_.
The form and disposition of the segments in _Textularia elongata_,
is shown in _Lign. 119, fig. 3_. These cells are filled with
inorganic matter. The shell of a Rosalina filled with an opaque mineral
substance, forming casts of the cells, is represented in _Lign. 119,
fig. 1_.
The preservation of the soft parts of foraminifera and of mollusks, in
a fossil state, is a phenomenon of frequent occurrence, and no longer
questioned by geologists, notwithstanding the scepticism with which my
first announcement of the fact was received. Dr. Bailey, of West Point
Military Academy, soon after the publication of my first paper, sent me
specimens from the marls of New Jersey.
Foraminiferous Limestones of India.--So much doubt was expressed as to
the accuracy of my opinion respecting the nature of the fossil Rotaliæ,
that its corroboration by observations on certain limestones in India,
by H. J. Carter, Esq. Secretary of the Bombay Royal Asiatic Society,
was as gratifying as unexpected. According to the researches of that
gentleman, the south-east coast of Arabia is chiefly composed of two
distinct limestone formations; the one averaging about 4,000 feet above
the level of the sea, and the other 600 feet. The latter forms the
desert of Akaf, and with the intervention of the mountains of Oman,
which belong to the greater formation, passes up into the lower Sindh;
while the former constitutes the high land of the coast, which, parting
from the western border of the Desert of Akaf, extends nearly to Cape
Aden.
The limestones of both these groups, or formations, consist chiefly of
foraminifera; the largest forms being visible to the naked eye. Mr.
Carter states that his attention was first directed to the organic
composition of the Porebunder limestone, which is imported into Bombay
for building, by small amber-coloured specks on the stone, that
resembled the soft parts of foraminifera figured and described by me
in the Philosophical Transactions. "On subjecting a portion of the
limestone to the action of acid, I found them to be what Dr. Mantell's
observations had led me to expect, the actual remains of the animals,
of exquisite beauty in form and symmetrical development. The minute
kinds in the Porebunder stone do not average more than 1/900 of an inch
in diameter; and the composite forms are held together by thread-like
attachments, which indicate the tubular communications that existed
between them when living."[331]
[331] "On the Existence of Beds of Foraminifera, Recent and Fossil, on
the South-East coast of Arabia," by H. J. Carter, Esq.; Proceedings of
the Bombay Royal Asiatic Society, 1848,
[Sidenote: FORAMINIFEROUS DEPOSIT AT CHARING.]
Foraminiferous Deposit at Charing. _Lign. 109._--The little town of
Charing, in Kent, has acquired a celebrity among those naturalists who
are interested in the present inquiry, by the researches of William
Harris, Esq. F.G.S. who some years since made known the existence of
a remarkable deposit of chalk detritus, about one foot in thickness,
which extends over the outcrop or exposed surface of the firestone in
that locality.
This bed consists of a soft, whitish, tenacious clay, which, when
immersed in water, is found to be largely composed of minute grains,
that prove to be foraminifera. These shells belong to many species
and genera; and are associated with the cases of entomostraceous
crustaceans, spicula of sponges, &c. The organisms readily separate
from the amorphous particles by washing, and specimens may be easily
obtained as distinct and perfect as if recent. See _Lign. 109_, _ante_,
p. 342. Intermingled with the cretaceous forms, are minute fresh-water
shells, apparently derived from a modern source.
The Charing deposit appears to have originated from the action of water
on the unconsolidated chalk of the neighbouring Downs, before the
surface of the hills was protected by a covering of vegetable soil.
Through the liberality of Mr. Harris, I have been able to examine an
extensive series of the Charing Foraminifera; and Prof Williamson has
figured and described the principal types in an interesting memoir in
the Transactions of the Manchester Philos. Soc. vol. viii. 1847. As in
most of the cretaceous strata, the prevailing species are referable to
the genera Textularia, Rotalia, Rosalina, Cristellaria, Lagena,[332]
&c. There are numerous spicula of sponges, and needle-like calcareous
prisms, which are the detritus of the fibrous shells, called Inoceramus.
[332] This interesting type of Foraminifera is the subject of a Memoir
by Prof. Williamson; Annals, Nat. Hist. 1848, vol. i.
Foraminifera of the Oolite, Lias, &c.--The occurrence of certain genera
in particular rocks has been incidentally noticed in the previous
descriptions, and it is needless to particularize any localities of
the Oolite, Lias, and other secondary deposits. It must suffice to
state that Dr. Carpenter, Prof Williamson, Prof Phillips, Mr. Sorby,
Mr. Rupert Jones, and other able observers, have figured and described
foraminifera from the strata between the Chalk and the Carboniferous
formations: the report to be drawn up by the two first-named gentlemen
for the British Association, will present a resume of the British
fossil genera and species.
It is deserving record, that no vestiges of foraminifera have been
found in the Wealden strata; the fluviatile origin of those deposits
renders it improbable that the remains of these marine organisms should
occur in great numbers, yet from, the estuary character of some of the
beds, the presence of foraminifera might be expected.
Foraminiferous Deposits of the United States.--Dr. Bailey has made us
familiar with the foraminiferous rocks of North America. The various
memoirs on this class of fossil animalculites, and on the diatomaceæ
(_ante_, p. 93), published in the American Journal of Science, and in
the Smithsonian Transactions, attest the acumen, and unwearied spirit
of research, of this able observer. Not only from the United States,
but from numerous localities in Asia and Arabia, Dr. Bailey has
transmitted me specimens of limestones containing foraminifera, chiefly
of the genera Rotalia and Textularia.[333]
[333] From Beyrout, Damascus, the Mount of Olives, Anti-Libanus.
In the calcareous marls of the Upper Missouri river, extending nearly
to the Rocky Mountains, similar fossils are met with.
In the interior of Florida, the white orbitoidal limestone is traversed
by flint; and the calcareous and siliceous masses are full of
microscopic foraminifera.[334]
[334] Smithsonian Contributions, vol. ii. p. 161.
[Sidenote: FORAMINIFERA OF THE CARBONIFEROUS FORMATIONS.]
Foraminifera of the Carboniferous Formations.--In the carboniferous
limestones of England, the late Mr. Bowman, Prof. Tennant, and Mr.
Darker, detected shells of foraminifera, apparently of the genus
Fusulina.[335] Prof. Phillips mentions the occurrence of nautiloid
foraminifera in the palæozoic limestones of Carrington Park, South
Devon, and Yorkshire.[336]
[335] Edinburgh New Phil. Journal, vol. xxx. p. 44.
[336] Proceedings of the Polytechnic Society of the West Riding of
Yorkshire, 1845.
Dr. Dale Owen is said to have obtained "well characterized polythalamia
from the oolitic portion of the carboniferous (Pentremitic, _ante_,
p. 298,) limestone of Indiana."[337] And M. de Verneuil discovered a
species of Fusulina, in the Millstone-grit of the coal formation of the
Ohio.
[337] American Journal of Science, vol. xlvi. note to p. 311.
But the most remarkable deposits of foraminifera in the palæozoic
rocks, are those of Russia, described by Sir Roderick Murchison.[338]
The upper beds of the Mountain limestone in the Lower Volga, consist
of laminated calcareous shales, composed of an aggregation of shells
of Fusulinæ. Bands of limestone, through a vertical extent of two
hundred feet, are loaded with Fusulinæ; layers from five inches to five
feet in thickness, consist of a pure white Fusulina limestone; the
foraminifera are all of one species, the _Fusulina cylindrica_.
[338] Geology of Russia in Europe, vol. i. p. 86. pl. i. fig. 1.
Foraminiferous Limestone of New Zealand.--"On the eastern coast of
the Middle Island of New Zealand, to the north of Otago, strata
of yellow and fawn-coloured limestone appear on the surface at
Ototara, and continue to Kakaunui. This rock is generally friable and
porous; it contains terebratulæ, spines and cases of echinoderms,
pseudo-belemnites, teeth of sharks, &c. A microscopical examination
shows it to be in a great part composed of an aggregation of very small
polythalamia."[339] The specimens of the Ototara limestone received from
my son, are very rich in minute corals and shells, and foraminifera
of the European cretaceous type: species of Rotalia, Cristellaria,
Globigerina, Textularia, Rosalina, Nodosaria, Dentalina, &c. Among them
are two forms which occur at Charing: namely, _Rosalina Lorneiana_,
_Lign. 109, fig. 5_, and Textularia elongata: of the latter a
specimen in flint is figured, _Lign. 119, fig. 3_. The soft parts of
Rotaliæ are preserved in the Ototara limestone, as in our chalk.
[339] Notes on the Geological Structure of the Middle Island of New
Zealand, by Walter Mantell, Esq. of Wellington. 1848.
There are likewise, as at Charing, cases of Entomostracæ of the genera
_Basidia_ and _Cythereis_.[340]
[340] See Geol. Journal, vol. vi. p. 339. pl. xxix.
The assemblage of fossil remains in the Ototara rock has decidedly a
cretaceous aspect, but till the geological position of the strata in
relation to the other formations of the Island is determined, it would
be premature to regard these limestones as the equivalents in time of
the Chalk formations of Europe.[341]
[341] A list of the Ototaran fossils collected by Mr. Walter Mantell, is
given in Geol. Journal, vol. vi. p. 329.
Tertiary Foraminifera.--The marine tertiary deposits which contain
foraminifera in abundance, are so numerous, that it is unnecessary to
particularize any. The sands of the Paris basin in some localities are
so full of microscopic forms, that a cubic inch of the mass contains
sixty thousand. The friable calcareous strata at Grignon are a loose
aggregate of the shells of foraminifera and minute mollusks; and as the
fossil shells from that locality are very common, and generally filled
with debris, the student will have no difficulty in obtaining specimens
for examination. The tertiary argillaceous deposits of England are less
rich in foraminifera than the arenaceous; but the usual types occur in
the London Clay, at Highgate, Clapham Common, Bracklesham Bay, &c. The
Eocene marls of the United States are rich in foraminifera.
[Sidenote: FORAMINIFERA OF THE FENS.]
Foraminifera of the Fens of Lincolnshire and Cambridgeshire.--Though
the alluvial deposits of the fen-districts are comparatively of modern
date, yet the rich assemblage of foraminifera contained in the clay
of certain districts is so interesting and instructive, that a brief
notice of them must not be omitted. The foraminiferous character of
the Lincolnshire alluvium was first made known to me by specimens from
Bolton, sent me by Professor Williamson; and their extension over
a wide area in Cambridgeshire, by a liberal supply from Mr. Smith,
of March. The bed that abounds in these shells, is about seven feet
beneath the surface, and consists of a fine sea sand combined with
carbonaceous and argillaceous matter. By washing about a gallon of this
earth in water, an ounce of polythalamia and organic detritus may be
obtained. The perfect shells are as fresh as if just dredged up from
the sea; the soft parts--the membranous segments held together by their
tubular connexion--in many instances remaining in the shell; these
parts may be obtained by the solution of the shell in acid. When the
Rotaliæ are rendered transparent by immersion in Canada balsam, their
appearance, by transmitted light is identical with that exhibited by
the fossil specimens; and if viewed by reflected light, the body may
be seen occupying all the cells of the shell; but the segments are
somewhat collapsed; evidently from the shrinking of the animal tissues
after death.[342]
[342] Two specimens are figured in my notice of fossil Foraminifera.
Phil. Trans, p. iv. for 1846, pl. xxi. figs. 13, 14.
The organisms of the Lincolnshire alluvium have been thoroughly
investigated by Prof. Williamson; they comprise many species and
genera, of the usual types; as Rotaliæ, Rosalinæ, Polystomellæ,
Textulariæ, Lagenæ, Nodosariæ, &c. It is remarkable, that though a
marine estuary deposit, no vestiges of diatomaceæ have been observed.
The bed so rich in foraminifera, extends west and south-west of the
Wash. Mr. Smith sent me a mass of sandy clay, from a well sunk in the
town of March, to the depth of twenty-five feet, that was loaded with
these beautiful organisms.[343]
[343] The reader interested in these inquiries should peruse the highly
interesting Memoir by Prof. Williamson, "On some Microscopical Objects
found in the Mud of the Levant, and other Deposits." Manchester Phil.
Trans, vol. viii.
Recent Foraminiferous Deposit at Brighton.--An interesting fact
connected with the phenomena under review is deserving record. The
presence of the fossils of an older formation, in strata subsequently
deposited, and in part composed of the detritus of the rocks whence the
organic remains were derived, is not uncommon: such fossils are termed
by the French geologists "_fossiles remaniés_." The nature of these
re-deposited fossils is generally obvious; either by the water-worn
condition of shells, bones, &c. or from their containing particles of
their parent bed; or if casts, from their mineral composition. Thus
in the chalk of St. Catherine's Mount, near Rouen, there are numerous
casts of Ammonites, Scaphites, and other shells, composed of marl full
of particles of greensand. These have evidently been washed out of the
preceding cretaceous beds of firestone or glauconite; and re-deposited
in the chalk strata in which they are now imbedded.[344] * * * * *
[344] M. D'Orbigny.
Along the sea-shore, to the east of Brighton, there is a bank of
sand and calcareous mud, the detritus of the neighbouring cliffs,
in the progress of formation; and in this sediment Mr. Reginald
Mantell discovered recent Rotaliæ, Nodosariæ, &c., with frustules
of Bacillariæ, Coscinodisci, Naviculæ, and other diatomaceæ;
associated with cretaceous polythalamia washed out of the chalk,[345]
The difference in the aspect of the recent and fossil organisms
was so evident, as to leave no doubt of the correctness of this
interpretation. Here, then, at the present moment, a deposit is going
on, whose organic contents consist of an assemblage of species of
living animalcules of our seas, with the fossil forms of the ancient
chalk ocean; in like manner as in the bed of the Nile, the Nummulites
of the tertiary rocks are being imbedded with the existing mollusks and
desmidiæ of that river (_ante_, p. 345).
[345] See _ante_, p. 99.
[Sidenote: GEOLOGICAL DISTRIBUTION OF THE FORAMINIFERA.]
Geological distribution of the Foraminifera.--According to the
observations of M. D'Orbigny, the first appearance of the tribes of
minute beings which have played so important a part in the elaboration
of materials for the formation of the sedimentary rocks of the
secondary and tertiary ages, and are at this moment invisible but
powerful agents in the accumulation of calcareous sediments at the
bottom of the sea, was in the Carboniferous epoch, and by a single
type, the _Fusulina_ (_ante_, p. 346). I believe no certain evidence
of the occurrence of Foraminifera in Silurian or Devonian deposits has
been obtained.
M. D'Orbigny gives the following summary of the distribution of the
known fossil and recent species:--
GENERA. SPECIES.
Carboniferous System 1 1
Jurassic 5 20
Cretaceous 34 280
Tertiary 56 460
Living in the present Seas 68 1000
Of the recent species, 575 inhabit the Tropics.
------ 350 ----- Temperate zones.
------ 75 ----- Cold regions.
The above statistical view was published six years ago; but the great
activity of research that has since prevailed, has largely augmented
the known number both of fossil and recent forms. M. D'Orbigny's recent
Tables[346] give for the Jurassic or Oolite 10 genera; Cretaceous, 38
genera; Tertiary, 60 genera; but this estimate must be far too low.
[346] Cours Elémentaire de Paléontologie.
* * * * *
I have thus endeavoured to convey a general idea of the highly
important results obtained by the microscopical investigation of the
minute organisms that enter so largely into the composition of many of
the fossiliferous deposits.
Without the aid of the most perfect optical instruments which modern
science and art have produced, even the existence of many of these
structures could not have been demonstrated; and we cannot doubt, that
were the powers of the microscope increased, the fossil remains of
beings still more minute would be detected; and that rocks and strata
which now appear to consist of amorphous particles of lime, of silex,
and of iron, would prove to be the aggregated skeletons of animals,
yet more infinitesimal than those which have formed the subject of our
contemplations. How strikingly illustrative are these phenomena of the
profound remark of the illustrious Galileo--"_La nature fait beaucoup
avec peu, et ses opérations sont toutes également merveilleuses._"
INSTRUCTIONS FOR THE MICROSCOPICAL EXAMINATION OF CHALK, FLINT, AND
OTHER ROCKS.
[Sidenote: MICROSCOPICAL EXAMINATION OF CHALK.]
Chalk.--The following method is that recommended by M. Ehrenberg, Place
a drop of water upon a plate of thin glass, and put into it as much
scraped chalk as will cover the fine point of a knife, spreading it
out, and leaving it to rest a few seconds; then withdraw the finest
particles which are suspended in the water, together with most of the
liquid, and let the remainder become perfectly dry. Cover this dried
spot of chalk with Canada balsam (the turpentine of _Abies balsamea_),
and hold the plate of glass over the flame of a lamp, until the balsam
becomes slightly fluid, without froth or air-bubbles; it should be
maintained in this position (the glass being kept as hot as the finger
will bear) for a few minutes, until the balsam is found to have
thoroughly permeated the substance to be examined. It is preferable
to place a piece of very thin glass upon the balsam, and gently press
it down, and allow it to remain. The best flatted crown-glass should
be used for placing the chalk or other objects on. It is convenient
to have the slips of glass of one size, or the specimens will require
different boxes for their reception; three inches by one inch is that
usually employed. These objects require to be viewed with a power
magnifying three hundred times linear, that is, in diameter; and if the
process has been properly conducted, it will be seen that the chalk is
chiefly composed of well-preserved organisms. In these preparations
the cells of the foraminifera appear at first black, with a white
central spot; this is caused by the air contained in those cavities,
for air-bubbles always appear as black annular bodies; by degrees,
the balsam penetrates into all the single cells, the black rings
of the air vesicles disappear, and the structure of the original is
beautifully displayed.[347]
[347] Specimens of chalk, flint, and other rocks for examination; or
specimens prepared on slides, may be obtained of the microscopic
artists, named in the Appendix.
Soft part of Rotaliæ in chalk.--The manner in which I obtained the
unmineralized soft bodies of foraminifera from chalk has already
been mentioned (_ante_, p. 360); but it may be useful to offer a
few additional suggestions; for such fossil remains are not easily
extracted. Many experienced microscopical observers have not succeeded
in obtaining one good specimen; but others have been more fortunate, or
persevering.
In several glass test-tubes, (the more the greater chance of success,)
put a few grains of chalk powder: pour the tube half full of diluted
hydrochloric (muriatic) acid--about ten parts water to one of
acid--agitate, and set the mixture by: when all action has ceased add
one or two drops of undiluted acid to each tube, and repeat the process
at due intervals till all the calcareous matter is dissolved. Pour
off the fluid, substitute distilled water, agitate, and then let the
sediment subside. The residue will consist of atoms of quartz and other
insoluble mineral matter, and animal tissue, if there be any. Then,
with a camel-hair pencil, place a small portion of the sediment on a
glass slide, and when dry cover it with Canada balsam, and treat it as
above directed. Among a dozen slides thus mounted, there will probably
be two or more good examples of the body, or detached membranous
segments of Rotaliæ or Textulariæ, like those figured in _Lign. 118_.
Calcareous Sandstones and Marls.--These substances may be examined by
the same process; but if of loose texture, Dr. Bailey recommends that
some of the sandy powder should be spread very thinly on a plate of
glass, with or without water, and by the aid of a lens of moderate
power the roundish grains should be selected and picked up with fine
forceps, or the point of a needle, and transferred to another piece of
glass, having on one spot a thin coat of Canada balsam. This should
be gently heated over a spirit lamp, when the balsam will penetrate
the grains, and render them transparent; by this process the minutest
shells, &c. may be detected. For a hasty exploration, the dust may be
rendered sufficiently transparent by a drop or two of oil of turpentine.
Sandy calcareous marls may be examined by diffusing a few grains in
water in a wine-glass, the lighter portions will be suspended in the
fluid, and may be placed on glass, and when dry prepared with Canada
balsam in the usual manner.
[Sidenote: MICROSCOPICAL EXAMINATION OF FLINT.]
Flint.--Flint, and other siliceous stones, require to be chipped into
very thin fragments, and immersed in oil of turpentine. A clear,
translucent flint should be selected, from which fragments may be
shattered off by smart blows of a hammer, over a sheet of white paper:
the most transparent flakes are to be selected, and these should be put
in oil of turpentine, in a wide-mouth glass bottle. Take out the pieces
for examination with forceps, and inspect them as transparent objects,
by transmitted light. When good specimens are discovered, mount them in
Canada balsam.
It is hazardous to entrust such fossils to the lapidaries; an
interesting group of twenty spiniferites was reduced to ten, by one of
our best workmen, in whose hands it was placed for polishing, with the
view of rendering it more transparent.