FOSSIL ZOOPHYTES.--PORIFERA OR AMORPHOZOA--POLYPIFERA OR
CORALS--BRYOZOA OR MOLLUSCAN ZOOPHYTES.
Many tribes of the extraordinary beings whose mineralized relics are
the immediate subject of our investigation, have largely contributed
to the solid materials of which the sedimentary strata are composed.
In the most ancient rocks in which vestiges of organic structures have
been detected, those of _Zoophytes_ hold a conspicuous place; and in
the seas of tropical climates, the agency of the Coral-animalcules, or
Polypifera, is producing enormous deposits, and laying the foundations
of new islands and continents, and forming reefs of rocks hundreds of
miles in extent, which, if elevated above the level of the sea, would
rival in magnitude the mountain-chains of modern Europe.
The reader unacquainted with the natural history of these marvellous
creatures will find an account of their nature and economy, and of the
physical effects produced on the earth's surface by their agency, in
the sixth lecture of _Wond._ vol. ii. p. 588.
The term Zoophytes, or animal-plants, comprises two very distinct
classes of living beings, namely, the Porifera, or Sponges, which (if
not vegetables) are wanting in many attributes regarded as essential
characteristics of the members of the animal kingdom; and the
Polypifera, or polype-bearing-animals,--the Corals; which are generally
associated groups or aggregations of individuals, united by a common
organized mass or axis, each polype having an independent existence,
and exhibiting volition and perception, in a greater or lesser degree.
Fossil Porifera.
[Sidenote: FOSSIL PORIFERA.]
The terms _Amorphozoa_ (signifying animals of variable shapes), and
_Porifera_ (structures traversed by pores or channels), are employed
by naturalists to designate the Sponges and analogous organisms,
which appear to occupy the boundary line that separates the animal
from the vegetable kingdom. The true position of the Sponges in the
great system of Creation is still a disputed point; for while many
distinguished naturalists regard them as _Protozoa_, or the lowest type
of animal organization, others of equal eminence affirm that neither in
structure nor functions do they differ from vegetables in any essential
particular; and that if a line be drawn between the two kingdoms the
Porifera must be placed on the vegetable side of the boundary. On
the other hand, Dr. George Johnston, in his delightful work on the
British Zoophytes,[193] expresses his opinion that there is nothing to
discountenance the belief that these bodies hold an intermediate place;
that they are, in fact, the true _Zoophytes_, or animal-plants; in some
forms, as the green _Spongillæ_ of our lakes, the vegetable nature
prevails; while in others, as the horny or keratose sponges filled
with mucilaginous slime, and the fleshy _Tethya_ whose oscula, or
pores, are said to exhibit signs of irritability, the animal character
predominates.
[193] A History of British Sponges, &c. by Dr. George Johnston,
Edinburgh. 1843. One vol. 8vo. with twenty-five plates. A previous
work, "A History of British Zoophytes," with forty-four plates, from
drawings by the accomplished lady of the Author, cannot be too highly
commended.
Without committing ourselves to either opinion, and simply remarking
that the large proportion of silex that enters into the tissues of
a considerable number of the porifera, is more characteristic of
vegetable than of animal structures, we proceed to consider the fossil
sponges and allied forms, as the mineralized remains of the lowest
types of the animal kingdom: if the vegetable nature of the originals
were generally admitted, this section should have followed that which
treats of the Diatomaceæ (_ante_, p. 100).
Sponge consists of a reticulated fibrous mass, covered with numerous
pores of various sizes, which are connected internally by anastomosing
channels, and this tissue is surrounded by a cellular gelatinous
matter, by which the entire structure was secreted, and is, in fact,
the vital part of the zoophyte. The tough framework or skeleton is in
some kinds fibrous, horny, flexible, or rigid, and strengthened by
calcareous or siliceous spicula (_spines_);[194] while in other species
its substance is calcareous, and in some siliceous, constituting a web
of transparent rock crystal, resembling spun glass,[195] The gelatinous
matter lines all the cavities, and forms the margins of the openings;
it presents no signs of irritability, and may be easily pressed out of
the porous mass with the hand, so slight is the connexion between the
skeleton and the investing tissue. Currents of water constantly enter
the small pores, traverse the inosculating canals, and issue from the
larger orifices, which often project above the surface in perforated
papillæ. By the circulation of the water through the porous structure,
the nutrition of the organized mass is effected; and the modifications
observable in the number, size, form, and disposition of the pores,
channels, and orifices, in different species, appear to be subservient
to this especial purpose; the imbibition and expulsion of water being
the only function the sponges perform. In its earliest stage the sponge
gemmule is of a spheroidal shape, and covered with vibratile cilia, and
after expulsion from the canals in which it is formed, moves rapidly
through the water till it becomes attached to some body, and is then
immovably fixed during life; exhibiting no signs of vitality save the
aqueous circulation through the pores and canals.
[194] The Mediterranean and American sponges of commerce are devoid
of spicules, and are deprived of their soft animal matter simply by
washing freely in fresh water.
[195] I particularly allude to a siliceous Sponge from Barbadoes, named,
by Mr. Samuel Stutchbury, formerly of the Bristol Institution, (now of
Australia.) _Dictyochalix pumicea_. This specimen is of a fungiform
shape, and appears to the naked eye as if formed of pumice stone, but
under the microscope is literally a tissue of transparent silex.
There is much confusion in the arrangement and nomenclature of the
fossil species of this class of zoophytes; and this has originated, in
part, from the varied forms assumed by the same species, having been
described under different names; and from the reprehensible practice of
changing, without sufficient reason, the name assigned to a species by
the original discoverer; an evil, unfortunately, not restricted to this
department of natural history.
The recent Sponges are arranged in four groups according to their
structure, viz.--
_Fresh-water Sponges._
Spongilla: siliceous spicula in a translucent jelly-like mass.
_Marine Sponges._
Tethea: having a tough outer skin; siliceous spicula in bundles, and
radiating from the compact nucleus to the periphery.
Halichondria: (from _silex_ and _cartilago_) siliceous spicula in a
cartilaginous mass.
Grantia: calcareous spicula in a gelatinous mass.
[Sidenote: FOSSIL SPONGES.]
M. D'Orbigny seems to believe that with the exception of the
horny _Cliona_, all the fossil sponges had originally calcareous
skeletons,--"qu'ils n'ont jamais été cornés, mais que leur tissu a
toujours été calcaire et pierreuse;"[196] which is certainly not the
case, for abundant examples of fossil keratose sponges occur.
[196] Cours Elémentaire de Paléontologie, torn. ii. p. 208.
I have selected a few genera for the illustration of the subject, and
shall describe them under the names that are most familiar to the
British scientific collector: doubtless sooner or later some competent
naturalist will undertake the elucidation of this department of
palæontology, and construct a classification and nomenclature based
on natural characters; till then the student will find it hopeless to
attempt to learn the ever-varying names of genera and species applied
to fossil Porifera and Polypifera, by different observers.[197]
[197] It has happened most unfortunately, that but recently Mr.
Lonsdale, in the late Mr. Dixon's beautiful work on Chalk and
Tertiary Fossils, and Mr. Milne Edwards in his able Monograph in the
Palæontological Society's Memoirs, have described many of our chalk
Corals under different specific and generic names.
[Sidenote: SPONGITES IN CHALK AND FLINT.]
On the Sponges in Chalk and Flint.--From the durability of the tissue
of the flexible sponges, and the imperishable nature of those which
have a siliceous or calcareous endo-skeleton or framework, their fossil
remains generally occur in a fine state of preservation, and in immense
quantities, in the sediments that were deposited in those parts of the
ancient sea-bottoms, originally inhabited by these zoophytes. Even the
relics of the keratose species, the _Halichondria_, whose structure
consists of siliceous spines imbedded in a cartilaginous mass, are
equally abundant. Sponge-spicula are everywhere met with in the chalk,
flint, and greensand, and many layers in the cretaceous strata are
almost entirely composed of them.
Sponges so commonly form the nuclei of the nodular flints, that some
naturalists have ascribed the formation of the layers and nodules
of silex in the cretaceous rocks to these zoophytes: a supposition
altogether groundless,[198] The various states of mineralization in
which sponges occur in the chalk give rise to many beautiful and highly
instructive fossils, as we shall point out in the course of this
notice. In general the zoophyte is simply invested by the flint, the
pores and tubes being filled with silex, the original tissue appearing
as a brown reticulated calcareous mass. In other examples the sponge
has been permeated by the liquid flint, and subsequently perished; and
in this manner have been formed those hollow nodules which on being
broken are found to contain only a powder, consisting of siliceous
spicules and fragments of silicified sponge. But in numerous instances
the substance of the zoophyte is completely silicified, and the
intimate structure of the original exquisitely preserved; such are many
of the flint-pebbles, and moss-agates, that are mounted as brooches and
other ornaments.
[198] See Wonders of Geology, p. 300. This question is fully considered
in a Memoir entitled Notes of a Microscopical Examination of the Chalk
and Flint of the South-East of England, &c. by the Author, in 1845.
Spongites.[199]--This name I would apply generically to those fossils
which appear to be identical in structure with the ordinary marine
sponges that consist of a fibro-reticulated porous mass, destitute of
regular tubes or canals: the form exceedingly various.
[199] _Achilleum_ of Schweigger.
The fossil sponges of the chalk may be divided into two groups; the
cyathiforms, or cup-shaped, and the ramose, or branched. Flints
inclosing the first kind, generally exhibit externally the form of
the original; those containing the branched species are of irregular
shapes, and except by an experienced observer, the nature of the
enclosed body would not be suspected. On breaking them, the sponge is
often well displayed, as in the specimen figured in _Lign. 69, fig.
2_: the surface of this fossil was covered with a white gritty powder,
made up of minute needle-shaped siliceous spicula.
[Sidenote: SPONGITES IN FLINTS.]
Spongites Ramosus.--A branched sponge, sometimes from twelve to fifteen
inches long, is not uncommon in the flints of the Lewes and Brighton
chalk; the stems and branches are cylindrical, and the terminations
of the latter are rounded and full of large pores. When completely
silicified the structure can only be detected by fracture, but
occasionally the sponge appears to have been saturated with liquid
chalk before it was enveloped in the flint; and as it is coated with
calcareous matter, it may be detached from the nodule entire.[200]
[200] In this manner I obtained the beautiful specimen (now in the
British Museum) figured in my Foss. South Downs, tab, xv. fig. 11. A
branch of this species is represented Pict. Atlas, pl. xxxix. fig. 12.
_Spongites lobatus_ (sp. Fleming) is figured Pict. Atlas, pl. xxxix.
fig. 6.
[Illustration: Lign. 69. Coral, and Spongites.
_Chalk. Sussex._
Fig. 1.--Petalopora pulchella. Upper figure × ×: lower figure, _nat._
_Chalk near Chichester._ (_Mr. Walter Mantell._)
2.--Spongites clavellatus. a branch in the cavity of a flint.
_South Downs._
3.--Siphonia Morrisiana. (G. A. M.) A transverse polished section
of a pebble. _Brighton Beach._
]
A smaller ramose spongite, with numerous short clavate protuberances,
is often met with in the flints of Sussex and Wilts; a branch is
figured in _Lign. 69, fig. 2_.[201]
[201] This spongite is named Polypothecia clavellata, in Miss Benett's
Wiltshire Fossils.
Spongites Townsendi. (_Pict. Atlas_, pl. xli.)--The cyathiform flints,
whose shape depends on the inclosed zoophytes, so much resemble the
cup-shaped sponges of commerce, as to be easily recognized in the
heaps of nodules that are collected in chalk districts for the roads;
they are from one to eight inches in diameter at the upper part, and
many are of a globular or spheroidal shape; the surface has the usual
calcareo-siliceous coating of flint nodules, giving a sensation of
roughness to the touch; the margin of the cup generally exhibits a
narrow band of porous structure, and when broken, sections of the
enclosed body are exposed. These funnel-shaped spongites terminate at
the bottom in a peduncle, whence fibrous root-like processes diverge;
by these appendages the original was fixed to the rock. I have
collected a few specimens in which the roots are attached to a shell,
or pebble, but have never seen any that appeared to occupy the spot
on which they grew. They seem to have been detached from their native
sites by the waves, and transported to a distance, and subsiding into
the tranquil depths of the ocean, became imbedded in the cretaceous
sediments that were accumulating at the bottom.
Spongites (?) labyrinthicus.[202] _Lign. 80, fig. 5._--Another
abundant species of amorphozoa has given rise to sub-hemispherical
flints, rounded below and flat above, with a marginal band of porous
tissue, that expands into flexuous lobes which fill up the area of
the upper surface. When found imbedded in the chalk, the form of this
zoophyte is often preserved entire; the upper part showing the lobated
and flexuous character of the original. Upon breaking these flints,
the organic structure is generally apparent; but in many instances
has perished, and left a cavity which is either partially filled with
stalactitical chalcedony, or lined with quartz crystals. These fossils
vary in size from a walnut to that of an orange; the pedicle has long
processes.
[202] Foss, S. D. tab. xv. _fig._ 7.
A lobed zoophyte, resembling the above in its general form, and
long rootlets, is distinguished by a large central cavity, which is
continued above the body in the form of a cylinder.[203]
[203] Beautiful figures of these and other chalk zoophytes are given
by Mr. Toulmin Smith in his elegant memoir "On the Ventriculidæ."
The specimens above described are named _Bracholites_ by Mr. Smith.
The plan of the present work forbids the discussion of that author's
opinions and inferences.
Spongites (?) flexuosus. _Lign. 80, fig. 10._--Among the
cyathiform flints that abound in the chalk, a very elegant species
is distinguished by a flexuous band that runs round the margin, and
indicates the lobed structure of the original.
In the chalk of Flamborough Head, Yorkshire, many beautiful cyathiform
sponges are preserved, in which the outer surface is thickly covered
with projecting hollow papillæ; these fossils are generally silicified,
the surface and pores being frosted over with minute quartz crystals.
The museum of the York Institution contains a splendid series of these
spongites.[204]
[204] The silicified state of these zoophytes was first detected by Mr.
Charlesworth, who by immersing specimens in dilate hydrochloric acid,
obtained admirable examples of the delicate structure of the original.
[Sidenote: FOSSIL ZOOPHYTES OF FARINGDON.]
Fossil Zoophytes of Faringdon. _Lign. 70, 71, 72._--The richest
locality for fossil sponges in England is in the immediate
neighbourhood of the little town of Faringdon, in Berkshire.[205] The
Greensand beds that overlie the Oolite in that district, consist of
a coarse friable aggregation of sand, comminuted shells, corals,
amorphozoa, and echinoderms, more or less consolidated by a ferruginous
cement. The gravel-pits, as the quarries are locally termed, expose
what evidently were banks of detritus thrown up on the strand of a
sea-margin; among the water-worn and fragmentary relics of oolitic as
well as cretaceous forms, many perfect sponges of various kinds may be
collected in the course of a few hours. Figures of some of the common
species are subjoined.
[205] See Excursions, in vol. ii.
[Illustration: Lign. 70. Fossil Zoophytes.
Fig. 1.--Lunulites radiatus. _Preston Chalk-pits_; view of the convex
side. (_Mr. Walter Mantell._)
1_a_.--Front view; _nat._
1_b_.--Portion of the surface of fig. 1, magnified.
2.--Scyphia intermedia; 1/2 _nat._ _Faringdon._
3.--Lithododendron sociale: the left-hand branch shows a vertical
section at the upper part, displaying the internal structure;
1/2 _nat._ _Mountain Limestone, Yorkshire._
4.--Verticillipora anastomosans. _Faringdon._
5.--Scyphia ramosa; 1/2 _nat._ _Faringdon._
6.--Scyphia foraminosa; 1/2 _nat._ _Faringdon._
7.--Cnemidium astrophorum; 1/3 _nat._ _Faringdon._
]
Scyphia. _Lign. 70, 72._--These spongites are of a tubular, fistulous,
or cylindrical form, and terminate in a rounded pit; they are either
simple or branched, and composed of a firm reticulated tissue; _Lign.
70, fig. 2, 5, 6_, and _Lign. 72, fig. 4_, are examples. The Upper
Greensand at Folkstone and Dover abounds in a flexuous species, named
Scyphia meandrina (_Morris_).
Cnemidium (_Goldfuss_). _Lign. 70, fig. 7._--These sponges consist
of a cluster of turbinated projections, having a central pit above,
and being porous on the external surface, and radiated at the margin.
The mass is dense and fibrous, and is traversed by horizontal canals,
diverging from the centre to the circumference.
[Illustration: Lign. 71. Fossil Sponge; _nat._
(_Chenendopora fungiformis._)
_Greensand. Faringdon._]
Chenendopora.[GX] _Lign. 71._--The species of porifera thus named
are cyathiform, or cup-shaped; externally furrowed, mamillated, or
lobed; internally smooth, and the surface covered with fine pores.
The beautiful species figured (_C. fungiformis_) is abundant in
the gravel-pits, and well known to the quarrymen as "petrified
salt-cellars."
[206] The Pictorial Atlas contains coloured figures of the following:--
Chenendopora fungiformis (_Michelin_), Pict. Atlas, pl. xliv. _fig._ 5:
according to Mr, Morris.
------------ subplana (_Michelin_), ibid, pl. xliv, _fig._ 3.
Scyphia articulata (_Goldfuss_), ibid, pl. xliii. figs. 7, 8, 9.
------- costata (_Goldfuss_), ibid. pl. xliv, fig, 1.
Cnemidium rimulosum (_Goldfuss_), ibid, pl. xliv. _fig._ 3.
[Illustration: Lign. 72. Fossil Zoophytes; _nat._
_Greensand. Faringdon._
Fig. 1.--Tragos peziza.
2.--Probably Chenendopora in a young state.
3.--Verticillipora anastomosans.
4.--Species of Scyphia.
5.--Tragos Faringdoniensis.
]
Tragos. _Lign. 72, fig. 1._--These turbinated sponges are readily
distinguished from the preceding, by the relatively large oscula, or
open papillæ, disposed irregularly on the inner surface; as shown in
the specimen, _fig. 1._ Their tissue is dense and fibrous. The fossil
represented by _fig. 5_, though named Tragos by collectors, appears
to differ in the structure of the inner surface from the type of this
genus: it is a remarkably beautiful species.[207]
[207] It may be convenient to distinguish it as _T. Faringdoniensis_.
The base in all these Greensand sponges is flat and expanded; not
fibrous and root-like, as in the spongites of the chalk previously
described.
Among the shingle at Brighton, Margate, Dover, Isle of Wight, &c.
pebbles containing fossil sponges may frequently be discovered. When
the flint nodule has been broken, and the calcareous particles of
the inclosed zoophytes are washed away by the action of the waves,
a delicate silicified tissue remains.[208] Many of the large solid
pebbles, are portions of silicified sponges, and polished specimens are
beautiful objects under the microscope.
[208] The pebbles represented in Pict. Atlas, pl. xlv. fig. 5, 12, are
specimens of this kind.
[Sidenote: SIPHONIA.]
Siphonia. _Lign. 73._--These fossil porifera are readily distinguished
from those which have engaged our attention by their more symmetrical
structure. The body of the zoophyte is a mass of dense porous tissue,
of a pyriform or bulbous shape, supported by a slender stem fixed
at the base by rootlets. The stem is composed of very fine parallel
longitudinal tubes, which extend to a series of canals that traverse
the mass, and terminate in openings on the surface of a shallow central
cavity, as shown in the section, _fig. 2, Lign. 73_. The characters
of this genus are well exemplified in a common species of the Greensand
(_S. pyriformis_, _Lign. 73_), described by the late Mr. Webster, from
specimens collected in the Isle of Wight, where it occurs in profusion,
near Ventnor, and the Western lines. This zoophyte is pyriform,
(_Lign. 73, fig. 1_,) and has a shallow cylindrical cavity, supported
upon a long slender stem, the base of which is fixed by root-like
processes (_fig. 5_); the transverse fracture shows a section of the
longitudinal tubes. This species has been found in numerous localities
of the Greensand, and also in the Firestone or malm-rock.[209]
[209] Dr. Fitton's figures, Geol. Trans. vol. ii. pl. xv. _a_, are very
beautiful and accurate.
The Portland limestone contains numerous remains of a Siphonia closely
resembling this species; and varied sections of its stems produce the
white markings commonly observable on the slabs of pavements.
[Illustration: Lign. 73. Siphoniæ, from the Greensand; _nat._
_Wilts, and Isle of Wight._
Fig. 1.--Siphonia pyriformis; the body or upper part.
2.--Vertical section of the same, showing the internal structure,
and the central cavity.
3.--Specimen of S. pyriformis in a young state.
4.--Siphonia (_Polypothecia_, of Miss Benett,) lobata; Firestone or
Upper Greensand, Warminster.
5.--The lower part of the stem, and radicles, of S. pyriformis.
]
A group of Sponges from the Upper Greensand, near Warminster, figured
and described by the late Miss Etheldred Benett,[210] under the name of
Polypothecia, comprises several forms that are allied in structure to
the Siphoniæ. These fossils present considerable diversity of shape;
one of the lobed forms is delineated in _Lign. 73, fig. 4_: and a
branched species in _Lign. 74_. Upon breaking the stem of one of these
zoophytes transversely, sections of parallel longitudinal tubes like
those in the Siphoniæ are exhibited.
[210] An elegant Memoir on the Wiltshire Fossils, by this accomplished
lady, is published in Sir R. C. Hoare's "Wiltshire."
[Illustration: Lign. 74.
Polypothecia dichotoma.
_Upper Greensand, Warminster, Wilts._]
The Kentish rag contains irregular ramose spongeous bodies, which
belong to this group of porifera; and Mr. Bensted has discovered
in his quarry, near Maidstone, numerous remains of a polymorphous
lobed zoophyte, having a porous structure beset with spicula. In the
Firestone of Southbourne, Steyning, and Bignor, in Sussex, I have
observed large pyriform and subcylindrical Siphoniæ.
The organization of all these zoophytes was evidently adapted for the
imbibition and circulation of sea-water, in a more perfect and definite
manner than in the irregular simple sponges.
Flint-pebbles inclosing remains of Siphoniæ abound on the Sussex
coast, especially in the shingle near Brighton, having been washed out
of the chalk cliffs. There were several chalk-pits in Edward-street,
(now, I believe, filled up and the area built upon,) in which every
flint enveloped a sponge or siphonia; many specimens were mineralized
by pyrites and beautifully exhibited the internal structure of the
originals.
Siphonia Morrisiana. _Lign. 69, fig. 3._--A polished slice of a
pebble from Brighton, whose markings are derived from the transverse
section of an undescribed zoophyte is figured, _ante_, p. 224: though
scarcely more than half the diameter of the original is preserved,
yet its structure is well shown; the centre is occupied by numerous
parallel openings, the sections of longitudinal tubes, and is
surrounded by a broad zone of spongeous tissue.
I have seen many examples of this beautiful fossil, set for brooches in
the jewellers' shops in the Isle of Wight, and at Brighton.[211]
[211] The specific name is in honour of John Morris, Esq. F.G.S. the
author of the "Catalogue of British Fossils," whose important services
to Palæontology and Geology it is gratifying thus to acknowledge.
There are coloured figures of Siphonite in Pictorial Atlas, pl. xxxix.
_fig._ 9; pl. xlii. _fig._ 3, 4, 5, 7, 12, and 13; pl. xliii. _fig._ 6.
Siphoniæ (chiefly _S. pyriformis_) are abundant in the Upper Greensand,
near Farnham in Surrey, but their tissues are saturated with phosphate
of lime, instead of silica as is ordinarily the case; the entire sponge
usually contains between 50 and 60 per cent, of phosphate: hence these
fossils have, of late, been in great request for manure.[212]
[212] Mr. Payne, of Farnham, a distinguished agriculturist, has largely
made use of them, both in the natural state and treated with sulphuric
acid. The Firestone strata on St. Catherine's Hill, Isle of Wight,
have been dug for a like purpose. See an "Account of the Phosphate
Diggings," in my Isle of Wight, Second Edition, p. 448.
[Sidenote: CHOANITES KÖNIGI.]
Choanites Königi, _Lign. 75._--The zoophyte which has given rise to
the fossils I have distinguished by the name of Choanites,[213] is of
a spheroidal or sub-ovate form, and appears to have been composed of
a softer tissue than the ordinary sponges. It has a central cavity,
and was fixed at the base by long rootlets: its mass is traversed by
numerous tubes or channels, which open on the inner surface of the
cavity; it differs from Siphonia in not having a stem composed of
bundles of tubes, and probably also in its constituent substance.
Among the Sussex and Wiltshire chalk-flints specimens of this zoophyte
are very common; they are easily recognized by the peculiar markings
produced by the silicified tubes that radiate from the centre, as seen
in _Lign. 75, fig. 4_. The semi-diaphanous pebbles on the Sussex
coast, more frequently contain Choanites than any other zoophytes. From
the beautiful and varied markings observable in the polished sections,
they are in great request for brooches, and are termed _petrified
sea-animal flowers_[214] by the lapidaries; among the shingle on the
sea-shore at Bognor, Worthing, and other places, very fine examples may
be collected.
[213] Foss. S. D. p. 178.
[214] From the supposition that the original was an _Actinia_, or
_Sea-Anemone_. A coloured vertical section of a pebble of this kind
is figured in my "Thoughts on a Pebble," Eighth Edition, pl. ii. See
coloured figures of Choanites in Pict. Atlas, pl. xlii. _fig._ 1, 9,
and 10; pl. xliv. _fig._ 8; and pl. xlv. _fig._ 10.
[Illustration: Lign. 75. Choanites Königi. (G. A. M.)
_Chalk, Lewes._
Fig. 1.--Transverse section of a siliceous specimen.
2.--Upper portion of a _Choanite_, in chalk, showing the opening
of the central cavity at _a_.
3.--Vertical section of a Choanite, in flint, exposing a section
of the mass, and canals passing obliquely from the
central cavity, through the substance.
4.--Choanite in flint; the usual appearance of these fossils.
5.--Various kinds of Spicula of fossil sponges; _magnified_.
]
_Lign. 75, fig. 4_, represents the usual appearance of a flint
deriving its form from a Choanite; _fig. 2_, is the upper part of a
Choanite preserved in chalk, and richly coloured by iron; the opening
at the summit, _a_, is the orifice of the central cylindrical cavity,
which is in this instance filled up by chalk, but in flint specimens,
with silex of a different colour to that of the surrounding mass.
If _fig. 2_, were placed on the top of _fig. 4_, the general shape
of the original zoophyte would be represented. The opening at the
base of _fig. 4_, marks the spot whence the processes of attachment
proceeded. The vertical section of a flint, similar to _fig. 4_, is
shown at _fig. 3_; and in this example are seen the central cavity,
and a section of the substance of the zoophyte, which is traversed
by numerous tubes, that ramify through the mass of which the body
was composed, and terminate in openings on the inner wall of the
central cavity, or sac. A transverse section of a similar flint is
delineated in _fig. 1_; the central white spot indicates the sac filled
with flint, and the tubes are seen radiating from it through the
mass; under a powerful lens the interstitial structure appears to be
granular rather than porous. The perfect transparency of the body when
silicified, and the rich tints it has acquired from metallic solutions,
and the compressed state in which it is often found, seem to indicate
that the original mass was a soft gelatinous substance, like that
of the _Actinia_, strengthened by spicula; for numerous tri-radiate
spines, like those on the left-hand of _fig. 5, Lign. 75_, occur
occasionally in chalk specimens.
In many Choanites, which differ in no other respect from the present
species, vertical sections show on each side the central cavity,
large oval spots, that are sections of a canal which traverses the
entire mass, proceeding from the base to the summit, in a spiral coil
around the central cavity. This structure was first detected by Mr.
Cunnington. Mr. Woodward thinks this spiral tube is common to all the
Choanites, and constitutes a generic character; but so many examples
have passed under my examination in which no traces of such a canal are
perceptible, that it may be a specific difference.
Among the chalk amorphozoa whose true affinities are doubtful, is a
small turbinated zoophyte, which I would place provisionally under this
genus; it has a shallow central cavity, with a broad smooth margin, a
reticulated external surface, and radicle processes proceeding from the
base; see _Lign. 80, fig. 1_.
[Sidenote: PARAMOUDRA.]
Paramoudra. _Lign. 76._--This vernacular Irish term was introduced by
Dr. Buckland, in his account of some gigantic flints, thus popularly
named, that occur in the chalk near Belfast, and also at Whitlingham,
near Norwich. These fossils are of an irregular, oblong, spherical,
or pyriform shape, having a cavity above, which, in some specimens,
extends to the bottom; indications of a pedicle are seen at the base;
in short, they closely resemble, upon a large scale, the funnel-shaped
spongites, so frequent in the flints of the South Downs. Their
appearance _in situ_, is represented _Lign. 76_, from Dr. Buckland's
illustrations: _b_, is a single specimen, partly imbedded in the chalk,
and _c_, _d_, two of the fossils in contact, the pedicle of the upper
one lying in the cavity of the lower.
These bodies are from one to two or more feet in length, and from six
inches to a foot in diameter. The appearance, both of the outer and
inner surface, is that of the usual white calcareo-siliceous crust of
spongitic chalk-flints. Upon breaking them, no decided structure is
perceptible; but here and there, patches of red and blue chalcedony
occur, as in the Ventriculites and spongites in chalk-flints; the
originals were probably large goblet-shaped zoophytes, allied to the
sponges, but of so perishable a nature as to leave but few traces of
their organization, save their general form. Specimens may however yet
be found with the structure preserved, for many years elapsed after the
first discovery of flint ventriculites, before I obtained examples that
threw light on their origin and formation.
[Illustration: Lign. 76. "Paramoudra;" seen in a vertical section of a
Chalk-pit, near Moira.
(_The Very Rev. Dr. Buckland._ Geol. Trans, vol. iv.)
_a, a, a._ Layers of flint nodules, alternating with chalk strata,
_b._ A Paramoudra, imbedded in the chalk,
_c, d._ Two of these bodies in contact.
]
In the Devonian slates of Polperro some curious fossils, supposed
to be remains of fishes, have been ascertained by Prof McCoy to be
Amorphozoa, and are described by that eminent palæontologist under the
name of _Steganodictyum_.[215]
[215] "Synopsis of the Classification of the British Palæozoic Fossils,"
by Prof. Sedgwick and Fred. McCoy. 4to. Fas. 2, p. vii. pl. 2 A. 1852.
Clionites (_Morris_) _Lign. 130._--A recent parasitical sponge (first
described by Dr. Grant under the name of _Cliona_), consisting of a
fleshy substance, full of siliceous tubular pin-shaped spicula, gives
rise to those perforations with which oysters and other shells are
often completely riddled,[216] Certain bivalve shells in the cretaceous
seas appear to have been peculiarly obnoxious to the depredations of
similar zoophytes, and in consequence of the cavities left by the decay
of the sponge having subsequently been filled up by flint, a curious
series of fossil bodies has resulted, which we shall more particularly
notice hereafter. These fossils Mr. Morris has distinguished by the
name _Clionites_, to indicate their origin; they are not, however, the
silicified sponge, but inorganic casts, moulded in the excavations.
The common species is _C. Conybearei_: "cells irregular, somewhat
polygonal, with one or more papillæ; surface finely tuberculated;
connecting threads numerous."[217]
[216] For an account of the characters of the recent Cliona, see a
monograph by Mr. Hancock, Annals of Nat. Hist. May 1851.
[217] Ann. Nat. Hist. August 1851, pl. iv, fig. 8.
Spicula, or spines of Porifera. _Lign. 75._--Siliceous spicules, as we
have had occasion to mention, occur in immense quantities in some of
those deposits which abound in the remains of spongites. These spines
are tubular, and of various shapes; some are acicular, or needle-like;
others of a stellate form; many are tri-radiate or multi-radiate; and
some have the shape of a trident; a few of these fossils are figured
in _Lign. 75_. As the _Actinia_, _Gorgonia_, and _Alcyonia_, possess
spicula, some of the fossil spines may have been derived from those
zoophytes. The larger spicules may be discovered with a lens of
moderate power, or even by the unassisted eye; but all will amply repay
a microscopical examination, and the minutest can only thus be detected.
[Sidenote: SPINIFERITES IN FLINTS.]
[Illustration: Lign. 77. A group of Spiniferites in Flint.
(Seen by transmitted light.)
Fig. 1.--A thin-translucent chip of flint; _nat._
2.--The same magnified, and viewed by transmitted light; showing
a group of five Spiniferites.
3.--The same more highly magnified.
4.--Spin. ramosus; one of the animalculites seen in fig.
3, very highly magnified.
5.--Spin. Reginaldi; one of the same group; × 300
diameters.
6.--A variety of S. ramosus; another of the same cluster
of Spiniferites.
]
Spiniferites (_Xanthidium_, Ehrenb.). _Lign. 77._--I propose to
describe in this place those elegant and very minute bodies, that occur
in great numbers in the chalk and flint, and which, on the authority
of M. Ehrenberg, were regarded as identical with the siliceous
frustules of the genus of fresh-water Desmidiæ, named _Xanthidium_[218]
(_ante_, p. 91.) Later and more correct observations have proved that
the fossils under consideration entirely differ from their supposed
homologues; their original substance not being siliceous, but flexible
and membranous; and that instead of being spores of algæ, they are
probably the gemmules either of porifera, or of polypifera.
[218] Several recent species of Xanthidium are figured in _Plate IV._ of
this volume.
To avoid the perpetuation of the error by the retention of the
botanical name of a recent genus of plants, for fossils whose vegetable
origin is very problematical, and which are entirely distinct from
their supposed analogues, I would substitute that of Spiniferites,[219]
a term simply expressive of the general aspect of these bodies; that of
a globe or sphere beset with spines. The appearance of these fossils
will be understood by the examination of a group discovered by Mr.
Reginald Neville Mantell, in a fragment chipped off from a flint
pebble; and I will describe the mode by which these minute objects
were detected, as it offers a good practical lesson for the young
investigator.
[219] From _spina_, a spine, and _fero_, to bear.
The chip of flint is represented, of the natural size, in _Lign. 77,
fig. 1_; it was immersed in oil of turpentine for a short time, and
then placed on a piece of glass, and examined with a moderate power, by
transmitted light, the turpentine having rendered the translucent flint
almost as transparent as glass; this appearance is shown in _fig. 2_;
the organisms here represented are from 1/300 to 1/500 of an inch in
diameter. The half-inch object-glass was next employed, and _fig. 3_
gives the result. The quarter-inch object-glass, and a corresponding
eye-piece, were then substituted, and by the adaptation of a camera
lucida, _figs._ 4, 5, and 6, were delineated. As _fig. 5_ proved to be
a new species, it was named after its discoverer.
The specimens in flint, when rendered transparent and viewed by
transmitted light under a high power, as shown in _Lign. 78_, and
79, appear as hollow globular bodies, beset with spinous processes,
which in most species are fimbriated at the extremities. There is
considerable variety in the form and length of the spines. In _S.
Reginaldi_, these appendages are numerous, regular, short, and
relatively thick: in an elegant species discovered by the Rev. J. B.
Reade (_Lign. 79_) they are long and palmated: in other kinds they are
of intermediate size and proportions.[220]
[220] Excellent figures of several species are given in a Memoir by H.
H. White, Esq. of Clapham, in the Trans. Microscopical Society, vol. i.
p. 77.
[Illustration: Lign. 78.
Spiniferites Reginaldi.
(_Magnified 500 diameters_.)]
[Illustration: Lign. 79.
Spiniferites palmatus; in flint.
(× 500 _diameters_.)]
The apparently torn and collapsed state of the body and arms of some
examples first led me to doubt the siliceous nature of the original
substance; and on my discovery of the soft parts of foraminifera in
flint and chalk, Mr. Deane undertook to search for the so-called
Xanthidia in chalk, that these bodies might be subjected to chemical
analysis,[221] Mr. Deane succeeded in detecting all the usual species in
the Dover chalk, by digesting some chalk in dilute hydrochloric acid,
and mounting the residue in Canada balsam. In this state the shape of
the body is that of a depressed sphere; many of the specimens appear to
have a circular opening, and the arms or spines to be closed at the
extremities. Upon pressure under water between two pieces of glass,
they were torn asunder as a horny or cartilaginous substance would
be, and the spines in contact with the glass were bent. Some after
maceration in water several weeks became flaccid; a proof that they are
not siliceous.[222]
[221] A torn and apparently shrunken specimen from chalk, is represented
in my paper on Foraminifera; _Philos. Trans._ 1846, p. 465.
[222] Memoir on Fossil Xanthidia, by Henry Deane, Esq. Microscopical
Journal, 1846.
The real nature of these fossils must be regarded as still
undetermined: their prevalence in the chalk-flints whose forms are
derived from zoophytes, seems to countenance the supposition that the
Spiniferites are the gemmules or early state of animals of this family;
but I have never detected any organic connexion between them and the
porifera with which they are associated; it is possible they may be the
germs of the remarkable zoophytes we have next to examine.
* * * * *
[Sidenote: VENTRICULITES.]
Ventriculites.[223] _Lign. 80, 81, 82._--At every step of our review
of the fossil zoophytes, I find myself embarrassed by the conflicting
opinions entertained by naturalists, respecting some of the most
abundant of the extinct forms; arising from the imperfect state of
our knowledge as to the structure of the originals, which compels
a comparison with recent types, from which, perhaps, the fossils
differed essentially in their organization. This remark especially
applies to the zoophytes which have given rise to the fungiform flints
so well known to the inhabitants of the chalk districts of Sussex,
as "_petrified mushrooms_," from their close resemblance in form to
fungi: a specimen with this name inscribed on it in the cabinet of a
friend first drew my attention to these curious fossils. In _Lign.
80, figs. 2, 3, 4, 6, 7, 8, 9_, several flints of this kind are
represented; _figs._ 3, 6, 8, are fungiform; _fig._ 7, is the upper
part of a specimen, the stem having been broken off; _figs._ 2 and
4, are examples of the lower part of the zoophyte; in all, there are
openings at the base, and a groove on the margin or edge of the upper
part in which the structure of the inclosed fossil is visible; upon
breaking these flints, sections of a funnel-shaped body are exposed.
[223] Ventriculite; from _ventriculus_, a ventricle or sac.
[Illustration: Lign. 80. Flints, deriving their forms from Zoophytes.
_From the South Downs, near Lewes_; 1/6 _nat._
Fig. 1.--Choanites (?) Turbinatus.
2, 3, 4, 6, 7, 8, 9.--Flints, whose forms are derived from
Ventriculites, provincially called "_petrified mushrooms_."
5.--Spongites labyrinthicus.
10.--Spongites flexuosus.
]
The origin of these fossils will be understood by reference to the
four specimens delineated in _Lign. 81_. In _fig._ 3, a fungiform
flint, resembling _fig._ 6, of _Lign. 80_, is seen in the lower part
of a cup-shaped zoophyte; while above, and surrounding the flint, the
impression remains of the reticulated outer surface, deeply coloured
by a ferruginous tinge. In _fig._ 4, _Lign. 81_, a small turbinated
flint, resembling _fig._ 4, of _Lign. 80_, occupies the base, and three
rootlets are seen emerging from it at a. In _Lign. 82, fig. 1_, in
which the chalk has been removed so as to expose the outer surface of
the Ventriculite, a flint occupies the centre at c; above which, the
radiating reticulated structure is spread out on the chalk, _a_; the
base, with its roots, is shown at _b_.
[Illustration: Lign. 81. Ventriculites radiatus; 1/6 _nat._
_Chalk; near Lewes._
Fig. 1.--A perfect specimen in chalk, inverted, showing the external
reticulated surface; the apex of the base projects in the
centre.
2.--Specimen expanded, displaying the inner surface, studded over
with the openings of the cells or tubes.
3.--A Ventriculite in chalk; the lower part inclosed in flint.
4.--Portion of a Ventriculite; the stem towards the base is
enveloped in flint, and three radicle processes spread from it
into the surrounding chalk at _a_.
]
These specimens demonstrate that all the flints referred to,
have been moulded in the cavities of cyathiform zoophytes;
and that their diversity of figure has arisen from the amount
of silex that happened to permeate the organism; if but a
small proportion of silica in solution was present, then flints,
like _fig._ 4, were produced; if the quantity were sufficient
to fill up a considerable part of the tissues of the original,
fungiform flints, as _Lign. 80, fig. 3_, and _Lign. 81, fig. 3_, were
the result. The disciform flints originated from the expanded
examples, _Lign._ 81, _figs._ 1 and 2: and when the silex
was insufficient to silicify the entire zoophyte, an annular
flint, resembling a quoit, was formed.
[Illustration: Lign. 82. Portions of Ventriculites; 1/4 _nat._
_Chalk, near Lewes._
Fig. 1.--A specimen, in which the middle is inclosed in a flint _c_;
the external structure of the Ventriculite is seen at _a_,
expanded on the chalk; and the pedicle with its roots is
exposed at _b_. The figures are one-fourth the size of the
originals.
2, 3, 5.--Chalk specimens, showing the external structure of stems
of Ventriculites.
4.--A siliceous cast of the cavity of a Ventriculite covered with
papillæ, moulded in the orifices of the cells.
]
The form of the original was evidently that of a hollow inverted cone,
terminating in a point at the base, which was attached by fibrous
rootlets to other bodies. The outer integument was reticulated, that
is, disposed in meshes, like net-work; and the inner surface studded
with regular openings, apparently the orifices of tubular cells. The
substance of the mass appears to have been sufficiently flexible to
expand and contract without laceration. This opinion is based on the
fact, that in many specimens the zoophyte is a nearly flat circular
disc (_Lign. 81, figs. 1, 2_); and in others a subcylindrical pouch. In
the former state the outer reticulated structure is elongated, while
in the latter, it is corrugated; hence I am led to conclude that the
original possessed a common irritability, and was able to contract and
expand like many of the flexible polypiaria. The openings on the inner
surface are cylindrical, and very regular; the flints often present
sharp casts of them, which appear like rows of minute pillars. When the
flint filling up the cavity of a Ventriculite can be extracted, it is a
solid cone, studded with papillæ, the casts of the cells, as in _Lign.
82, fig. 4_.
In the flints, the substance of the Ventriculites is generally as
translucent as that of the Choanites, and defined by its rich purple,
sienna, or grey colour;[224] but towards the base and margin it is
more or less calcareous; and in many examples the whole, or a large
portion of the zoophyte, is in this state. But this fact does not
invalidate the inference that the original was flexible; for in these
instances the tissues may have been immersed in fluid chalk before
their envelopment in flint,[225] The chalk specimens are commonly as
friable and earthy as the surrounding stone, from which they are
distinguishable by their ochreous colour.
[224] Pict. Atlas, pl. xlv. _fig._ 9, represents a beautiful transverse
section of the lower part of a Ventriculite in flint, richly
coloured. Pl. xliii. _fig._ 16, is a pebble containing the base of
a Ventriculite; the orifices on the top have been produced by the
transit of the radicle processes; for the fossil is drawn in an
inverted position, a common error before the origin of these flints was
ascertained.
[225] A piece of sponge dipped in liquid plaster of Paris, and
afterwards inclosed in a transparent substance, as glass, would present
such an appearance.
The stain always observable in the tissues of the chalk Ventriculites
and other zoophytes, while the surrounding white limestone is
uncoloured, may be explained by the chemical changes to which the
decomposition of animal matter under such circumstances would give
rise. If sulphuretted hydrogen were evolved from the putrifying
zoophytes imbedded in calcareous mud containing iron in solution,
the sulphur would enter into combination with the iron, the hydrogen
escape, and a sulphate or sulphuret of iron be deposited, atom by atom,
and thus impart colour and permanence of form to the original.
When the inclosed organisms in the flint nodules have perished,
chalcedony, quartz crystals, or crystallized pyrites, sometimes of
great beauty, are found occupying the cavities; in short, numerous
modifications of the petrifactive process are beautifully exhibited in
these common, but highly interesting, cretaceous fossils.
The species to which the previous remarks more immediately refer, is
named _Ventriculites radiatus_; from the radiated appearance of the
external integument; some of the expanded specimens are more than one
foot in diameter.[226]
[226] The reader interested in the history of these objects should
consult Foss. South Downs, p. 167, plates x, xi, xii. xiii. xiv. A
memoir by the Author on these fossils, under the name of _Alcyonium
chonoides_, with four beautiful plates, was published in the Linnæan
Transactions, vol. xi. 1821. The _Ventriculites_ are the only organic
remains figured in Conybeare and Phillips's Geology of England and
Wales, p. 76.
[Illustration: Lign. 83. Ventriculites alcyonoides. _in Flint. Lewes._
_Ocellaria inclusa. König._
Fig. 1.--Portion of the surface of fig. 2, magnified.
2.--The fossil body extracted from the flint, fig. 4.
2_a_.--Transverse section of the same, showing a central
spot of flint, surrounded by tubular cells.
2_b_.--Two of the cells of fig. 2_a_, highly magnified.
4.--The hollow flint, from which fig. 2 was extracted; the papillæ
on the surface, are casts of the apertures of cells.
]
Ventriculites alcyonoides. _Lign. 83._--Under the name of "_Ocellaria
inclusa_," the late Mr. König[227] figured and described an elegant
fossil zoophyte not uncommon in the chalk and flints of Sussex. This
fossil is inversely conical, and somewhat resembles the cast of the
cavity of _Ventriculites radiatus_, but a little attention will
enable the collector to distinguish it. The flint that is moulded
in _V. radiatus_, is surrounded by the substance of the zoophyte,
and if found detached, with the investing material removed, shows no
structure whatever, but simply a surface covered with minute papillæ.
The present zoophyte is generally included in a nodule, and by a slight
blow may be readily separated from the surrounding flint; it then has
the appearance of a white calcareous cone, beset with regular cells,
disposed in quincunx order (_Lign. 83, fig. 2_); leaving a conical
cavity in the flint, which is covered with corresponding eminences
(_Lign. 83, fig. 4_). Upon breaking the cone itself, it is found to
consist of a dense reticulated structure, from one-eighth to a quarter
of an inch in thickness (_Lign. 83, fig. 2a_), investing a solid
nucleus of flint, the surface of the latter being covered with minute
points, which are less regular than those on the cavity of the outer
case. The specific name, _inclusa_, was suggested by this character;
which, however, is only accidental, for the specimens imbedded in
chalk, are simply surrounded by the stone. It is the calcareous nature
of the fossil, which renders it so easily separable from the investing
flint, while its cells afford numerous points of attachment, and these
remain as casts in relief on the interior of the hollow case: I have
not observed the same regularity of structure on the inner as on the
outer surface.
[227] Icones Foss. Sect. _fig._ 98.
The reticulated integument of this zoophyte resembles in structure
that of _V. radiatus_. With regard to the latter, I should state that
Mr. Toulmin Smith[228] discovered that the inosculating fibres of the
intimate tissue formed an octahedral plexus at each knot or point
of union; and this structure Mr. Smith regards as peculiar to the
Ventriculites, and states that he detected it in all the fossils he has
arranged under the name _Ventriculidæ_. No spicula have been detected
in the integuments.
[228] "On the Ventriculidæ;" a series of papers published in the Annals
of Natural History, with many figures of cretaceous zoophytes. By
Toulmin Smith, Esq.
Until more ample and satisfactory evidence is collected as to the
nature of these fossils, the interests of science will be best promoted
by allowing the question to remain sub judice, and restricting the term
Ventriculites to those zoophytes which possess the general characters
of the type to which the name was originally assigned; namely, a
vasiform or subcylindrical framework, terminating at the base in a
point, and fixed by radicle processes; the substance consisting of
a plexiform fibrous tissue; externally constituting a reticulated
integument, the meshes disposed in a radiating manner from the base
to the periphery; the inner surface studded with open cells regularly
arranged.
In the former edition of this work the Ventriculites were placed with
the Polypifera from the structure of the openings or cells, for these
are so symmetrical, and disposed with so much regularity, as to present
a closer analogy to the polype-cells of a coral, than to the large
pores of a sponge. The doubts expressed by many eminent observers as to
the correctness of this view, have induced me to insert this notice in
the present section; leaving the true affinities of these organisms to
be determined by future observers. Possibly we have in these fossils
the relics of a tribe of zoophytes of an extinct type, that formed a
connecting link between the _porifera_ and the _polypifera_; however
this may be, I will venture to affirm that no one who had seen the
infinitely varied examples of these fossils that I have, would for a
moment confound them, as some naturalists have done, with the Scyphiæ,
and other simple amorphozoa.
[Illustration: Lign. 84.
A Coral-polype in flint.
× 500 _diameters_.
(_Seen by transmitted light._)]
Polype in Flint. _Lign. 84._--I will here notice an exceedingly minute
and interesting object, discovered by the Rev. J. B. Reade, in a flint
containing vestiges of a Ventriculite, and which may possibly belong
to this tribe of zoophytes. It must however be remarked, that there
was nothing to show the collocation was not accidental. The drawing
with which Mr. Reade favoured me, is engraved _Lign. 84_. This object
is unmistakeably a polype-cell, with some of the integument of the
animal protruding, in the form of a shrivelled tube. The possibility
of soft animal tissues being preserved in flint, will not now admit
of question, as we shall show when treating of the Foraminifera. The
record of this fact may load to the discovery of other fossils of a
like nature.
Fossil Polypifera.
[Sidenote: POLYPIFERA.]
As we proceed in our investigations, the impossibility of rigidly
adhering to a zoological classification based on the structure of
organs, of which but few, if any, traces exist in the mineral kingdom,
becomes more and more apparent; the durable skeletons or polyparia
being the only materials from which the palæontologist can gather
information, relating to the physiology of the extinct coral-animals
which swarmed in the ancient seas, and whose petrified remains
constitute a large proportion of the secondary and palæozoic calcareous
rocks.
Numerous fossil genera have been established by various authors from
the external form of the polyparium, or the disposition and structure
of the cells; but a slight attention to this department of palæontology
will disclose corals which differ essentially from the typical forms,
and new genera and species will require to be added to the already
extended catalogue. The few genera selected for the present work,
will convey a general idea of the nature of this class of fossils. To
ascertain the names of the species he may collect, the student must
refer to works especially devoted to the illustration of the corals of
particular rocks; as for example, those of the British _Cretaceous_
deposits in the monographs of the Palæontological Society; of the
_Palæozoic_ in _Sil. Syst._; and in Prof Sedgwick's Synopsis of the
Classification of the Brit. Pal. Foss.; of the _Mountain Limestone_
in Prof, Phillips's work; and those of Ireland in Col. Portlock's
Geological Memoirs. Those of the palæozoic rocks of New York, are
illustrated in Prof. James Hall's splendid work on the Geology of that
State.
The fossil zoophytes included in this section present innumerable
varieties of form and structure, but agree in the important character
of having originated, (with but few exceptions,) from aggregations
of those minute beings termed Polypes (many-feet[229]). The common
Hydra (_Wond._ p. 600), or fresh-water polype, that inhabits pools
and streams, is a familiar example of a free animal of this kind,
consisting of a cellular gelatinous substance, in the form of a short
tube, or pouch, surrounded at the upper margin by long tentacula,
or feelers, which appear to the naked eye as delicate threads. The
_Polypifera_, properly so called, are groups of polypes, permanently
united by a common integument or axis, each animalcule having an
independent existence. A common support or endo-skeleton, termed
_polyparium_,[230] is secreted by the integuments, which varies in
its nature from a mere gelatinous, or horny material, to an earthy,
calcareous, and even siliceous substance, that remains when the polypes
die, and their soft parts have perished. All the varieties of corals,
&c. are nothing more than the durable structures of aggregated masses
of such beings.
[229] A name derived from the tentacula, or processes, which in some
species serve for prehension, and in others for respiration.
[230] The basis, framework, or endo-skeleton, of these groups
of animalcules is termed the _polyparium_, or _polypidom_
(polype-habitation); those of a stony hardness are familiarly known as
corals; these names, therefore, refer to the durable substance, and not
to the animals themselves; but in familiar writing, the term Coral is
often used to designate the entire living mass. The Red-Coral forms a
distinct genus called _Corallium_. In fossils, the _polyparium_ alone
remains, except in very rare instances.
It may here be necessary to notice a prevailing error, regarding the
mode in which the substance called coral is produced. It is very
generally supposed that Corals, particularly those bearing stars and
cells, have been constructed by animalcules, in the same manner as
is the honey-comb, by the Bee; and the expressions often employed
by naturalists, of "the coral animalcules building up their rocky
habitations," and "constructing their cells," have contributed to
foster this error. But the processes are in no respect similar: the
insect, under the guidance of an unerring instinct, resulting from
its peculiar organization, _constructs_ its cells; but the polype is
incapable of forming, or even modifying, its support or cell in the
slightest degree. The polypidom is _secreted_ by the animal tissues, in
the same manner as are the bones in the vertebrated animals, without
the individual being conscious of the process. If a piece of white
coral be immersed in dilute hydrochloric acid, the calcareous part is
dissolved, and the secreting membrane, in the form of a flocculent
substance, is seen attached to the undissolved part; even in some
coralline marbles of incalculable antiquity, the animal membrane may,
in this manner, be detected.[231]
[231] See Pict. Atlas, pl. xxxiv. _fig._ 2.
From the delicate and perishable nature of many of the gelatinous
zoophytes, numerous tribes may have inhabited the seas, which deposited
the fossiliferous strata, and yet no indications of their existence
remain; while, of others, but obscure traces of their structure are
likely to be detected.
The Polypifera are separated into two natural groups or classes; viz.
the Anthozoa (flower-animals), and the Bryozoa (moss-animals), or
Polyzoa.
The Anthozoa are polypes of the most simple type of structure. The body
consists of a symmetrical gelatinous sac, capable of contraction and
expansion, with one aperture or mouth, which is encircled by tentacula.
The Hydra, or fresh-water polype (_Wond._ p. 600), is a familiar
example of a single, locomotive, anthozoan animal. In the compound
or aggregated forms, the body is either inclosed in a horny sheath
(ex. _Sertularia_, _Wond._ p. 615), or is supported by a lamellated
calcareous endo-skeleton (ex. _Fungia_, _Wond._ p. 623, pl. vi. _fig._
15), or the soft parts invest a stony axis (ex. _Madrepora_, _Wond._ p.
620), or a horny flexible framework (ex. _Gorgonia_, _Wond._ p. 616).
The Anthozoa are subdivided into three orders, which are based on
the peculiar characters of the polypes; the _Hydra_, the _Actinia_
(Sea-Anemone, _Wond._ p. 622), and the _Alcyonium_ (Dead-men's fingers,
_Wond._ pl. v. _fig._ 10), being respectively the type of 1. the
_Hydroida_, or Hydraform; 2. the _Asteroida_ or Alcyonian; and 3. the
_Helianthoida_, or Actiniform zoophytes.
In the Hydroida the body in the compound species is implanted in a
horny tubular sheath, and the polypidoms form branched corallines,
which are fixed by the base to rocks, sea-weeds, shells, &c.
The Asteroida have a horny or calcareous axis, surrounded and inclosed
by the soft parts which secrete it.
The Helianthoids, except in the simple free species, as the Actinia,
have a lamellated calcareous polypidom, the plates of which radiate
from a centre.
The calcareous secretions of the Anthozoa, especially of the
Helianthoida, in a great measure constitute the mass of the coral-reefs
and coral-islands of tropical seas. Their polypidoms, whether external
or internal, maintain but little organic connexion with the compound
soft substance. These zoophytes increase by gemmation or budding; some
throw up germs from the disk, as in Astreadæ; others laterally, as in
Caryophillidæ; and some spirally along the stem, as in Madreporidæ;
examples of these modes of reproduction are often found in fossil
corals. The increase of coral-rocks is produced by the continual
formation of new masses, by the successive generations which spring up
as it were from the bodies of their parents; layer upon layer, and tier
upon tier, of Helianthoid polypidoms, are found to compose many of the
coralline limestones of the palæozoic formations.
Fossil Anthozoa.--The first group of extinct corals to be noticed under
this head is the _Graptolitidæ_, a family restricted to the Silurian
rocks, and whose natural affinities have been much questioned; some
palæontologists referring them to the _Pennatulidæ_, or Sea-pens,
others to the _Sertulariadæ_.[232]
[232] For a full consideration of this subject, refer to Prof. McCoy's
Brit. Palæozoic Fossils.
[Sidenote: GRAPTOLITES.]
[Illustration: Lign. 85. Graptolites in Wenlock Limestone.
(_Murch. Sil. Syst._)
Fig. 1.--Graptolites ludensis.[233]
1_a_.--Magnified view of a portion of the same.
2.--Graptolites Murchisoni.
2_a_.--Magnified portion of _fig._ 2.
]
[233] _Ludensis_, from Ludlow--to indicate the habitat of the fossils.
Graptolites. _Lign. 85._--These curious zoophytes abound in many of
the Silurian deposits; they consist of sessile polype cells, arranged
in one or two rows to a flexible stem, like the recent Sertularia, or
Virgularia. Prof. McCoy refers them to the order Hydroida.
In a recent state these bodies were probably covered with a soft, or
albuminous mass, studded with polype-cells, disposed in rows along
the margins of the lateral, curved, grapple-like processes, as in the
zoophytes termed _Virgularia_,[234] to which one kind bears a great
analogy. If two specimens of the _Graptolites Ludensis_ be placed
together, so that the elongated smooth edges be in apposition, the
united stems will be seen to offer a general resemblance to the axis of
_Virgularia mirabilis_.
[234] See British Zoophytes, pl. xxiv.
M. Barrande divides the Graptolites into three groups or genera, which
are defined as follow:--
_Graptolites_ (proper), a single series of cells united together at the
base, and adhering along the sides nearly to the orifice of each cell,
as in _fig. 1a_. _Monoprion_ of M. Barrande.
_Rastrites._--The axis reduced to a mere line, on which the cells are
placed at relatively wide intervals, and but slightly inclined. These
two genera are supposed to have been hydroid zoophytes, and related to
the Sertularidæ.
_Diprion_ (_Diplograpsus_ of Mr. McCoy), cells in two series arranged
along a central axis; these forms present a foliaceous appearance; they
are presumed to resemble the existing genera Pennatula and Virgularia.
Graptolites have been found in strata of the same age in Norway,
Sweden, and Scotland.[235] I have received slates literally covered with
them, from the Silurian rocks of the United States, by the kindness of
my friend, Benjamin Silliman, jun. Esq.
[235] Many species of Graptolites from the Lower Silurian rocks of the
South of Scotland, are described and figured by Mr. Harkness in Geol.
Journal for 1850, vol. vii. p. 58, pl. 1.
Sir R. Murchison remarks, that the nature of the strata in which these
remains occur in Radnorshire, indicates a condition of the sea, well
suited to the habits of the family of Pennatulidæ, or Sea-pens; for
the recent species live in mud and slimy sediment, and the fossils are
imbedded in a finely levigated _mud-stone_, which, from its structure,
must have been tranquilly deposited.
* * * * *
I will next describe the single lamellated Anthozoa, and afterwards
notice those corals which consist of an aggregation of radiated cells,
either frondescent, or disposed in solid masses.
[Sidenote: FUNGIA. ANTHOPHYLLUM.]
Fungia (_Wond._ p. 623).--The corals thus named, from their supposed
resemblance to fungi, are of a depressed form, and have the under
surface scabrous; they are divided above by numerous lamellæ, or
plates, which radiate from a central, oblong depression.
When living, the solid stony polyparium is enclosed in the gelatinous
mass by which it was secreted, and there are numerous tentacula
around the central cavity, or sac. These zoophytes may be compared
to the _Actiniæ_, or Sea-Anemones, from which they differ only in
having a calcareous axis, while the Actiniæ have a tough albuminous
integument. (_Wond._ pl. vi. _fig._ 15, represents the living animal;
and _Lign. 141, fig. 2_, p. 641, and _Lign. 58, fig. 4_, two fossil
species).[236]
[236]
Fungia numismalis. Pict, Atlas, pl. xxxvi. _fig._ 6.
------ polymorpha. Ibid. pl. xliii. _fig._ 1--4; pl. xlv, _fig._ 11.
Anthophyllum Atlanticum. _Lign. 88. fig. 4._--In the arenaceous
strata of the United States, which the researches of Dr. Morton,
of Philadelphia, have proved to be the equivalents of the European
Cretaceous formation, a single lamellated coral is not uncommon. It is
evidently related to the Fungiæ, and has been named as above by Dr.
Morton.
Turbinolia Königi (_Wond._ p. 320).--Polyparium turbinated, striated
externally, detached, base not adhering; cell single, radiated.
This genus occurs in all the fossiliferous deposits: a small,
well-marked species is frequently met with in the Galt, of which
subdivision of the cretaceous strata it is a characteristic fossil. It
is figured _Wond._ _Lign. 58, figs. 1, 2_.[237]
[237]
Turbinolia complanata. Ibid. pl. xxxvi. _fig._ 9.
---------- mitrata. Ibid. pl. xxxvi. _fig._ 10.
Caryophyllia centralis (_Lign. 89 figs. 1, 2_: _Lign. 88, fig.
5_).--Polyparium turbinated, or cylindrical, simple or branched,
longitudinally striated, fixed by the base; cells lamellated.[238]
[238] Monocarya (of Lonsdale), Dixon's Fossils, p, 244.
A small recent species (_C. cyathus_), is very common in the
Mediterranean, and frequently seen in collections: it is cyathiform,
and the base by which it is attached to other bodies, is broad and
spreading; the newer tertiary deposits of Sicily contain this species
in abundance.
A Caryophyllia, bearing a general resemblance to this species, is
common in the chalk, and occurs in beautiful preservation (_Wond._
_Lign._ 58, _fig._ 3).[239]
[239]
C. centralis, Pict. Atlas, pl. xxxvi. figs. 15, 16.
C. annularis, ibid. pl. xxxvii. _fig._ 5.
Branched Caryophylliæ are found in the Coralline Oolite and Dudley
Limestones (_Sil. Syst._ pl. xvi.). A large proportion of the Coral-rag
of the Middle Oolite is composed of a branched species (_C. annularis_)
of this genus; _Lign. 88, fig. 5_, represents a specimen from near
Faringdon.
[Illustration: Lign. 86. Favosites polymorpha. (Goldfuss.)
_Devonian limestone. Eifel._
Fig. 1.--Portion of a branch of the coral; _nat._
2.--Fragment, slightly magnified, with part of the surface broken
away below, exposing the central axis, and radiated
arrangement of the cells, with their lateral pores.
3.--Another portion, magnified, showing the polype-cells hollow.
]
Favosites polymorpha. _Lign. 86. Lign. 88, fig. 3._--Polyparium
stony, polymorphous, solid internally, compact, composed of a
congeries of diverging or ascending parallel, contiguous, prismatic
tubes, covered by pores, divided by lamellæ, and communicating by
lateral foramina.
The corals of this extinct genus abounded in the Silurian and Devonian
seas; the remains occur with those of other fossil zoophytes of that
epoch in great numbers, both in Europe and North America. I have many
beautiful examples from the Silurian rocks of the Ohio and Niagara, by
favour of Dr. Owen, of New Harmony, and Dr. Yandell, of Louisville, in
which the cells are filled up with calcareous spar. The varied markings
on many of the Babbicombe marbles, and Torquay pebbles, are derived
from the enclosed Favosites (_Wond._ p. 643).
Another species (_Favosites Gothlandica_) occurs in masses of a
subconical shape, and is common in some of the Silurian limestones. A
fragment, to show the structure, is figured _Lign. 88, fig. 3_.
[Sidenote: CATENIPORA. SYRINGOPORA.]
Catenipora (_Wond._ p. 644, _fig._ 3).--Polyparium hemispherical,
composed of vertical anastomosing lamellæ; cells tubular, oval,
terminal, united laterally. The oval form of the cells when united
laterally, and the flexuous disposition of the lamellæ, give rise
in transverse sections to elegant catenated markings, from which
appearance the fossil has received the name of _chain-coral_.[240] The
species figured (_C. escharoides_) in _Wond._ is common in the Silurian
limestones, and sometimes forms hemispherical masses more than a
foot in diameter. The chain-coral is extensively distributed through
the Silurian rocks of the United States. Coloured figures of this
exquisitely beautiful coral are given in _Pict. Atlas_, pl. XXXV.
[240] Org. Rem. vol. ii. pl. iii. figs. 4, 5, 6.
Syringopora ramulosa. _Lign. 88, fig. 2._ (_Wond._ p. 641.) These
corals bear a general resemblance to the Organ-pipe Coral of Australia.
The polypidom is composed of long, cylindrical, vertical tubes, distant
from each other, and connected by transverse tubular processes; the
cells are deep and radiated by numerous lamellæ.
The external aspect of these fossils is that of a cluster of
cylindrical pipes, more or less parallel, connected by short transverse
branches. They are the _Tubiporites_ of Mr. Parkinson, who has given
admirable figures of several specimens.[241] In these fossil corals
that excellent observer first detected the animal membrane. A slab of
marble, whose markings are produced by the section of the inclosed
tubes of a Syringopora, is represented, _Wond._ p. 644, _fig._ 2. The
Mountain limestones of Derbyshire, and of Clifton, on the banks of the
Avon, contain figured marbles of this kind, which are manufactured into
vases, tables, &c. The genus is extinct.
[241] Pict. Atlas, pl. xxxv. _fig._ 1. Syringopora geniculata, Pict.
Atlas, pl. xxxiv.
Lithostrotion Columnaria (_Wond._ p. 641, _fig._ 8).--Polyparium
massive, solid, composed of aggregated, contiguous, parallel, prismatic
tubes, each terminated by a star: cells shallow, multi-radiate,
stelliform.
Species of this extinct genus are common in the mountain limestone, in
large masses, which, from the pentagonal form, and parallel arrangement
of the tubes, appear like clusters of miniature basaltic columns.[242]
[242] Lithostrotion striatum, Pict. Atlas, pl. xxxvii. figs. 5, 6.
[Sidenote: CYATHOPHYLLUM.]
Cyathophyllum. _Lign. 87, figs. 1, 2._ (_Wond._ p. 641, _figs._ 1,
3.)--Polyparium turbinated, simple or compound, internal structure
transversely chambered or lamellated; cells polygonal, radiated,
depressed in the centre.
The corals of this genus are so abundant in the Silurian rocks,
that the seas of that epoch must have swarmed with them. The simple
turbinated forms are often several inches long, and being somewhat
curved, have obtained the popular name of "_petrified rams-horns_."
Upon slitting one of these corals vertically, as in _Lign. 87, fig.
1_, the axis of the polyparium, beneath the cell, is found to consist
of thin transverse partitions, constituting a series of chambers.
In the compound Cyathophylla, the germs of young cells, occupying
the disc of a parent cell, are often met with. _Fig._ 3 represents a
group of four germs on the parent cell, of _C. dianthus_, a common and
beautiful coral of the Dudley limestone.
[Illustration: Lign. 87, Corals from the Dudley Limestone.
(_Sil. Syst._)
Fig. 1.--Cyathophyllum turbinatum: an oblique longitudinal section,
showing at a the transverse lamellæ, or cells, of the internal
structure.
2.--The same species.
3.--Cyathophyllum dianthus: a Specimen, with four young germs
arising from the disc below.
4.--The same species, with four adult cells.
]
These corals are also prevalent in South Devonshire, and many of the
elegant marbles of Babbicombe are figured by the sections of these
polyparia.[243]
[243]
Cyathophyllum turbinatum, Pict. Atlas, pl. xxxvi.
------------- fungites, ibid. pl. xxxviii.
Associated with the Cyathophylla in the Silurian rocks, are certain
corals that attain considerable magnitude, and which are principally
distinguishable by their internal structure. Such are _Cystiphyllum_,
constructed of bladder-like cells, and _Strombodes_, composed of
spirally contorted lamellæ, or plates (_Sil. Syst._ pl. 16^(bis),
_fig._ 4). Other hemispherical masses, presenting on the surface
concentric wrinkles, with very minute pores, are common at Dudley, and
belong to the genus _Stromatopora_.
[Illustration: Lign. 88. Fossil Corals.
_Upper Silurian, Dudley._[244]
Fig. 1.--Astrea ananas.
1_a_.--A polished slice of Marble, formed of Astrea pentagona.
_Devonian. Torquay._
2.--Syringopora ramulosa. _Mt. L. Derbyshire._
3.--A Fragment of Favosites Gothlandica. _Ohio._ (_By Dr. Owen._)
4.--Anthophyllum Atlanticum. _Cret. U. States._ (_By Dr. Morton._)
5.--Caryophyllia annularis. _Oolite. Faringdon._
]
[244] Figured in Pict. Atlas, pl. xxxvii. _fig._ 1.
[Sidenote: ASTREA.]
Astrea. _Lign. 88, figs. 1, 1a._--Polyparium massive, irregular
in shape, generally globular, formed by an aggregation of lamellated,
radiated, shallow, polymorphous cells.
The corals of this genus are very numerous in the seas of the Tropics,
and there are many species in the Oolite, and older secondary
formations. The Astreæ, Caryophylliæ, Cyathophylla, &c., form the
principal mass of the coralline limestones of the Oolite, termed the
_Coral-rag_, from the abundance of these relics: being literally
composed of an aggregation of large corals, the interstices of which
are filled with shells, radiaria, &c., either whole, or in a comminuted
state. The heaps of this limestone placed by the road-side, in the
N. W. of Berkshire, appear like fragments of an old coral-reef, and
attract the notice even of the most incurious observer. I have figured
a specimen of Astrea, _Lign. 88, fig. 1_, and a polished section,
_fig. 1a_, from Clifton, a locality well known for the stupendous
mural precipices of mountain limestone rocks, which yield beautiful
examples of coralline marble.[245] The mode of increase of the Astrea
is very curious; a subdivision takes place in the old cells, after the
manner of the Infusoria; and among the fossils, a star or cell may
often be seen in progress of division into two, three, or four stars
(_Sil. Syst._ pl. xvi. _fig._ 6). A living polype of this genus is
figured, _Wond._ pl. vi. _fig._ 13.
[245]
Astrea arachnoides, Pict. Atlas, pl. xxxviii. _fig._ 4.
------ undulata, ibid, pl. xxxviii. _fig._ 10.
------ Tisburiensis ibid. pl. xxxviii. figs. 12, 13.
A species of Astrea (_A. Tisburiensis._ _Wond._ p. 641, _fig._ 9), is
found in large hemispherical masses, completely silicified, at Tisbury,
in Wiltshire. The transverse surface displays, in some specimens,
beautiful white radiated stars, on a dark blue ground; and in others,
the colours of the stars and ground are reversed. This silicified
coral is obtained from a bed of chert, a foot in thickness, which is
interstratified with the Portland limestone, this division of the
Oolite being quarried around Tisbury.[246]
[246] See Catalogue of the Organic Remains of Wiltshire, p. iv. by Miss
Etheldred Benett. 4to. 1831.
In the tertiary clays at Bracklesham Bay, Sussex, a beautiful small
coral of this type (_Siderastrea Websteri_, Dixon's Foss. tab. i, 5),
is found attached to flint pebbles.
Several species of this and the following genus, perfectly silicified,
are found in the state of pebbles and boulders in the superficial soil
of Antigua, and other islands of the West Indies, associated with the
fossil palms, described in a former part of this work. Some of these
corals are of great beauty, and polished sections exhibit the coralline
structure most perfectly.[247]
[247] In the "Spongitenkalk," at Nattheim, near Heidenheim, all the
corals are replaced by chalcedony.
Madrepora.--Polyparium arborescent or frondescent, porous, fixed;
cells deep, with twelve rays, prominent, irregularly dispersed on the
surface, and accumulated towards the terminations of the coral.
The term madreporite, or fossil madrepore, was formerly applied to all
the branched fossil corals with radiated cells, but is now restricted
to those which possess the above characters. The recent common species,
figured _Wond._ p. 620, will serve to illustrate this genus. The
elevated, branched Madrepores, with minute polygonal cells having
twelve rays, the lamellæ of which are denticulated, are termed Porites,
and are frequent in the Silurian strata (_Sil. Syst._).
Millepora. _Lign. 89._--Coral ramose; cells very minute, distinct,
perpendicular to the surface, giving the interior a finely striated
fracture, disposed irregularly.
There are many fossil species of this genus, some of which are of
considerable size. A small species from the mountain limestone is
figured _Lign. 89, fig. 7_.[248]
[248] Millepora, Pict. Atlas, pl. xl. _fig._ 6.
Lithodendron. _Lign. 70, fig. 3._--Polyparium branched, formed of
deep, cylindrical, elongated cells, which are terminal, and radiated,
with a prominent central axis.
Large masses of corals of this genus, composed of clusters of
branches, are imbedded in the mountain limestone of Derbyshire,
Yorkshire, &c.; and a few species occur in the Coralline Oolite; their
general configuration will be understood by the figure _Lign. 70,
fig. 3_; but in this specimen the margins of the cells are worn off,
and do not present the original deeply excavated form.[249]
[249] Lithodendron fasciculatum, Pict. Atlas, pl. xxxviii.
There is a remarkable specimen of this coral in the Bristol Institution
(of which a portion is now placed in the Museum of Practical Geology,
in London), that was discovered by Mr. Samuel Stutchbury,[250] in a
vein of hematitic iron ore. It is a large mass, in which the entire
substance of the coral is transmuted into a metallic ore, forming one
of the most interesting natural electrotypes I have ever seen. In
this instance, a block of Lithodendron must have lain in a vein or
fissure of the rock, and its animal membrane have resisted the action
of the gaseous emanations, or mineral solutions, while the calcareous
polypidom was dissolved, and the metallic matter deposited atom by
atom, as in the case of pseudo-morphous crystals.
[250] Now of Sydney, Australia.
Gorgonia.--Of the flexible anthozoan coral, which from the flabellated
form of the polyparium is generally called "Venus's fan," and by
naturalists _Gorgonia_, a few fossil species have been discovered and
determined. From the friable arenaceous limestone beds of Maestricht,
which abound in corals, fine specimens of a delicate species are
occasionally procured. _Wond._ p. 320, _fig._ 5, shows the character of
this fossil zoophyte.
Fossil Bryozoa.
[Sidenote: FOSSIL BRYOZOA.]
The second class of Polypifera, the Bryozoa or _Polyzoa_, are of a
much higher order of organization than those which have engaged our
attention. The body is not symmetrical, nor capable of contraction and
expansion, as in the Anthozoa: it consists of a digestive cavity or
sac, which is bent on itself and open at both extremities. The outer
integument is either membranaceous or horny; sometimes calcareous. The
oral aperture or mouth is surrounded by a circle of tentacula, from
eight to twelve or more in number, and these tentacles are clothed with
vibratile cilia. (_Wond._ p. 606, the polype of _Flustra pilosa_.)
The polypes in this order never occur singly; they are always united
by a common integument, but each enjoys an individual existence. The
animal can extend its tentacula and protrude the mouth from the cell,
but the rest of the body is incapable of extension or contraction.
These polypifera increase by germination. In their organization,
they so closely approach the mollusca, that in recent zoological
systems they are placed in that class. The ciliated character of
their tentacula has also led to their being named _Cilio-branchiata_.
But as it is desirable in a work of this elementary nature to avoid
conflicting opinions as much as possible, the fossil Bryozoa will be
considered as corals, in the general sense of that term.
[Sidenote: FLUSTRA. ESCHARA.]
Flustra (_Sea-mat_). _Lign. 89, fig. 4, 5._--The polyparium is
either membranaceous and flexible, calcareous and encrusting, or
foliaceous, composed of cells, arranged in juxtaposition, more or less
quadrangular, flat, with a distinct border, disposed on a flat surface,
or on opposite surfaces, as in the _F. foliacea_.
This is one of the most common genera of the encrusting and frondescent
zoophytes. The _Flustra_ consists of a cluster, or aggregation of
polypes, invisible to the naked eye; under the microscope, the polype
is found to be a transparent gelatinous body bent on itself, with a sac
or digestive cavity, having two apertures, the external margin of which
terminates in eight or ten tentacula, clothed with cilia; the whole is
surrounded by a firm wall, constituting a cell, from which the animal
can protrude its tentacula and upper part. (Figures of the living
polypes of Flustræ, _Wond._ p. 605, _pl._ vi. _fig._ 6, 7.)
Many species of _Flustræ_ occur in the British strata: the encrusting
forms are attached to echinites, shells, &c.; the foliaceous are
imbedded in chalk, sand, sandstone, &c. In Mr. Morris's _Cat. Brit.
Foss._ ten species are enumerated; none of these are from formations
below the Chalk. I have selected for illustration a Flustra attached
to an echinite from Lewes. _Lign. 89, fig. 5_, represents a small
portion of the natural size; and _fig. 4_, a few cells magnified, to
show their form and arrangement. A foliaceous zoophyte, apparently a
bryozoon, is abundant in the Sussex and Kentish chalk, and is often
disposed in angular folds. It is generally of a ferruginous colour,
and, from its friable texture, it is probable the original consisted
of a membranous polypidom or calcareous substance; specimens sometimes
extend over several square inches of the chalk. It is common in the
chalk-pit at Off ham, near Lewes.[251]
[251] In my South Down Fossils, pl. xv. _fig._ 6, a specimen of this
kind is described as a Ventriculite, _V. quadrangularis_. An admirable
lignograph of a remarkable example is given by Mr. Toulmin Smith, under
the name of _Brachiolites angularis_; it presents ten deep, flat,
angular folds, and has radicle and lateral processes; see "On the
Ventriculidæ," p. 93.
Eschara.[252]--In these zoophytes the polyparium is encrusting or
foliaceous, calcareous and brittle; the cells are thickened on their
outer margins, and have a small, depressed, round aperture. They are
arranged in two series of planes, adhering together, the cells on each
surface exactly corresponding.
[252] So named from a supposed resemblance to an eschar.
Species of Escharæ are found either in flints, or attached to
echinites, and other bodies; they have the appearance of patches of
flustræ, but with a lens may be distinguished by the symmetrical
juxtaposition of the cells on the opposite sides of the polyparium.
[Illustration: _Ellen Maria Mantell, ad nat. delt._
Lign. 89. Corals from the Chalk and Mountain Limestone.
Fig. 1.--Carophyllia centralis; _nat._ (G. A. M.) _Cret. Lewes._
2.--Front view of half the disc of the same.
3.--Two cells of Crisia Johnstoniana. × ×.
4.--Magnified view of six cells of the Flustra, _fig._ 5.
5.--A portion of an encrusting Flustra; _nat._ _Cret. Chichester._
6.--Idmonea (Dixoniana) cretacea; _nat._ _Cret. Lewes._
The figure on the left shows the under surface; that on the
right, the upper surface, with a row of polype-cells on
each margin: a portion magnified is given _fig._ 12.
7.--Millepora rhombifera. × ×. _Mt. L. Ph. Yorks._
The small figure on the left is of the natural size.
8.--Pustulopora pustulosa. × ×. _Cret. Chichester._
The small figure on the left, _nat._
9.--Homœsolen ramulosus. × ×. _Cret. Dover._
The left-hand figure, _nat._
10.--Crisia (?) Johnstoniana. (G. A. M.) × 250 linear.
_S. s. Maidstone._
10_b_.--Two cells of the coral, _fig._ 10, seen in profile, × ×.
11.--Homœsolen ramulosus; _nat._ _Cret. Lewes._
12.--Idmonea Dixoniana; a portion of _fig._ 6. ×.
13.--Retepora laxa. _Mt. L. Ph. Yorks._
13†.--A portion of the same ×.
14.--Idmonea Comptoniana. × ×. (G. A. M.) _Chalk, Chichester._
(_Mr. Walter Mantell._)
The small figure on the right is of the natural size.
]
[Sidenote: MICROSCOPIC FOSSIL BRYOZOA.]
Crisia Johnstoniana. _Lign. 89, fig. 3, 10, 10b._--The minute
recent corals thus designated are allied to _Flustra_, but separated
from that genus by the cells being disposed in a single series, and
united by connecting tubes. I notice this genus to direct attention to
a very curious polypidom from the Greensand of Maidstone, presented to
me by Mr. Bensted. The specimen is attached to a fragment of shell. The
cells, five of which are represented, _fig._ 10, are elliptical, with
the aperture above, and towards one extremity; they are united by very
slender, hollow filaments: _fig. 3_, two of the cells seen from above
× 250 linear; _fig. 10b_ the same seen in profile.[253] I have named
this species _C. Johnstoniana_, as a tribute of respect to the author
of the admirable works on British Zoophytes, previously noticed.
[253] I refer this fossil to the genus _Crisia_ with some hesitation;
perhaps _Hippathoea_ would be more correct, but all the described
species of the latter are branched.
The fragmentary relics of numerous minute and elegant corals,
constitute a considerable portion of the mass of some of the white
chalk strata; several genera of these zoophytes are figured in Mr.
Dixon's beautiful work, and described by Mr. Lonsdale. Attached to
the surface of shells, &c., and sometimes standing erect in little
crannies, or hollows, of the flints, many beautiful corals may often be
detected with the aid of a lens. By brushing chalk in cold water, and
examining the deposit, the student will probably discover several of
the species figured in _Lign. 89_, which we proceed to describe.
Retepora (_Lace-Coral_). _Lign. 89, fig. 13._--A very thin calcareous
polyparium, disposed like net-work in foliaceous and branching plates;
cells opening either on the upper or inner side.
These are an elegant tribe of corals, of which many species occur in
the Chalk formation at Maestricht, in the white-chalk of England,
in the mountain limestone of Yorkshire, (_Phil. York._), and in
the Silurian deposits (_Sil. Syst._). It may be useful to state,
that in the description of the fossil retepores, the openings in
the net-work are called fenestrules--the spaces between the ends,
_dissepiments_--and those between the fenestrules, interstices. A
delicate fossil retepore from the mountain limestone of Yorkshire (_R.
flexa_), is figured _Lign. 89, fig. 13_.
Fenestrella.--Cells very small, indistinct externally, with small
prominent openings; polyparium stony, fixed at the base, composed of
branches, which inosculate by growth, and form a cup. Numerous delicate
corals, formerly arranged as _Reteporæ_, occur in the Silurian rocks,
and have been placed in this genus by Mr. Lonsdale. (_Sil. Syst._ p.
677.)
Petalæpora pulchella.[254] _Lign. 69, fig. 1._--This beautiful
cretaceous coral is "tubular, free except at the base; framework
composed of vertical laminæ, with an intermediate foraminated
structure; apertures to the tubular cavities distributed over the
surface; exterior varying with age." It has slender round dichotomous
branches, and the polyparium when entire must have formed an elegant
plexus of coral. A layer an inch thick, full of branches of this
zoophyte, is exposed on the face of the chalk cliffs, near Dover; and
beautiful masses, several inches square, made up of this coral, Idmonea
and Pustulopora, may be obtained. The microscopic specimen figured in
_Lign. 69_, was obtained with many other corals by washing chalk with a
brush, and examining the detritus deposited.
[254] Mr. Lonsdale. Dixon's Fossils, p. 285.
Pustulopora. _Lign. 89, fig. 8._--Another very common tubular
branched coral of the Dover chalk; the tubes are cylindrical, their
apertures are arranged in annular or spiral rows, and slightly
projecting, giving a pustulous appearance to the stem and branches.
Specimens covering a piece of chalk six or eight inches wide, and a
foot long, have been discovered. The example figured is a very minute
branch.
Homœsolen ramulosus.[255] _Lign. 89, figs. 9, 11._--This delicate
branched coral is formed of large and small tubes variously
intermingled, both inclined in the same direction, partially visible
on the surface, or wholly concealed, limited to one side of the coral;
mouths simple tubular extremities; back without pores, composed of a
continuous lamina.[256]
[255] Homœsolen, from ομοιος, similar; and σωλην, a tube.
[256] Mr. Lonsdale, in Dixon's Fossils, p. 307, tab. xviii. B. figs, 3,
4, 5.
The elegant coral, _fig. 11, Lign. 89_, is thus named by Mr.
Lonsdale; it resembles his _fig. 4_. The fossil, _fig. 9, Lign.
89_, though very different in its branching, and in the surface, which
is covered with pores, is evidently identical with _fig. 3_ of Mr.
Lonsdale, which he refers to the same species.
Idmonea, _Lign. 89, fig. 6._--In this elegant coral the polyparium is
calcareous, branched, porous; the cells distinct, prominent, arranged
in single rows, more or less inclined, on each side a median line on
the inner face only. The genus is extinct.
A beautiful species of Idmonea, of which a small branch is figured in
_Lign. 89_, abounds in the chalk of Kent and Sussex; it often forms a
cluster, two or three inches in circumference. The surface of the stems
is covered with minute pores, and the cells are distinct, and placed in
single rows; the left-hand figure of _fig. 6_ shows the plain surface,
and that on the right, the opposite and inner, each margin of which
is garnished with a row of cells; a portion magnified is represented
_fig. 12_.[257]
[257] In the former edition of this work, I named this species _I.
Dixoniana_, to commemorate the researches of my late friend, Frederic
Dixon, Esq., of Worthing, who had formed an interesting collection
of chalk fossils, and announced a work on the "Zoology of the Chalk
Formation," to be richly illustrated with figures of many undescribed
organic remains. It appears that a species, supposed to be identical,
had been previously named by Mr. Milne Edwards, _I. cretacea_. See
Dixon's Foss. tab. xviii. A. _fig._ 5, p. 281. Mr. Lonsdale places it
in a new genus, with the name of Desmeopora semicylindrica. It will
convey some idea to the unscientific reader, of the labour bestowed
on this department of palæontology, to learn that the description and
identification of but 25 species of minute corals, represented on three
plates, occupy ninety pages of close printing in royal 4to. of Mr.
Dixon's work.
Idmonea Comptoniana,[258] _Lign. 89, fig. 14._--This is a very small
and remarkable coral; it is dichotomous, cylindrical, with elongated
distinct cells, which are disposed in triplets, at regular distinct
intervals, on one side of the stem.
[258] This specific name is in honour of the noble and highly respected
President of the Royal Society, the Marquess of Northampton. 1844.
We have now described all the fossil corals figured in _Lign. 89_; and
have shown what interesting organisms may be detected in a few grains
of calcareous earth. It would be easy to give restored figures of the
beings whose stony skeletons are the subject of these remarks, from
their close resemblance to existing species; every pore and cell might
be represented fraught with life; here the agile inmates, with their
little arms fully expanded, and in rapid motion; there retreating
within their recesses, and devouring the infinitesimal living atoms
that constitute their food; or rapidly shrinking up their tentacula
upon the approach of danger; even their varied colours might be
introduced, and thus the beautiful and highly interesting picture drawn
by the imagination, of a group of living zoophytes of the ancient chalk
ocean, be presented to the eye.
Although, for convenience, I have selected the above examples
principally from the cretaceous strata, the reader must not suppose
that other deposits are not equally prolific in these remains. The
Coral-rag of the Oolite, many beds of the Mountain limestone, and
those of Dudley and Wenlock of the Silurian System, contain myriads
of minute polypidoms associated with the coralline masses of which we
have already treated. Exquisite figures of the Silurian corals, by Mr.
Scharf, are given in _Sil. Syst._ pl. xv. xvi. and described by Mr.
Lonsdale. A slab of the Dudley limestone often has the entire surface
studded with minute corals of many species and genera, lying in bold
relief, and in an admirable state of preservation.
Verticillipora (_Lign. 70, fig. 4. Lign. 72, fig. 3_).--Cells
poriform, arranged in meshes on the surface of convex imbricating
plates round a hollow axis, forming a fixed, irregular, subcylindrical
polyparium. _Lign. 70, fig. 4_, represents a coral often met with
in the gravel-pits at Faringdon, (_ante_, p. 228,) which is referred
by Mr, Morris to this genus. It is composed of short cylindrical
anastomosing tubular branches, emanating from an expanded base, divided
internally by transverse parallel plates, covered with exceedingly
minute pores or cells, disposed in meshes; the plates surround a hollow
axis; the structure is well shown in the figure.
Lunulites. _Lign. 70._--The polyparium is stony, orbicular, convex
above, concave below; concavity radiated; convexity covered with cells,
arranged in concentric circles on diverging striæ.
A species of this coral is often found in the chalk: _Lign. 70, fig.
1_, represents a specimen from the South Downs, discovered by Mr. Walter
Mantell. The natural affinities of this genus are not determined with
precision; but I have placed it with the Bryozoa in accordance with the
opinion of M. de Blainville. It is an elegant white coral, and easily
recognized among the minute organisms of the chalk.
* * * * *
[Sidenote: DISTRIBUTION OF FOSSIL BRYOZOA.]
Geological Distribution of Fossil Zoophytes.--Although the geological
distribution of fossil zoophytes affords less striking phenomena than
that of the vegetable kingdom, yet some interesting reflections are
suggested by the facts we have thus cursorily noticed. We find that
in the most ancient seas of which any vestiges of their inhabitants
remain, these forms of vitality existed, and produced the same physical
results as at the present time; giving rise to coral-reefs, and banks
of coral-limestones, and largely contributing to the solid materials
of the crust of the globe. Nearly 400 British species are enumerated
by Mr. Morris, and the list has subsequently been greatly extended by
the labours of Phillips, Portlock, Lonsdale, McCoy, Milne Edwards, and
other eminent naturalists.
The Tertiary formations afford numerous species of Caryophylliæ,
Flustræ, Escharæ, Spongia, &c.; and the _Crag_, several genera that
are as yet but imperfectly determined. The older Tertiary, or Eocene
deposits, contain Turbinoliæ, Astreæ, Fungiæ, Meandrinæ, and species
of other genera, the recent types of which are inhabitants of tropical
seas.
The zoophytes of the British Chalk have been illustrated in detail
by Mr. Lonsdale in Dixon's Cretaceous and Tertiary Fossils of the
South-East of England; and by Dr. Milne Edwards in the Monographs of
the Palæontological Society.
In the Maestricht deposits, lamelliferous corals, as Astreæ, Fungiæ,
Meandrinæ, &c. prevail, and may be extracted from the friable
arenaceous limestones in a fine state of preservation. In the White
Chalk and Greensand of this country, the Spongites and allied genera
are abundant, and associated with Caryophylliæ, Astreæ, and many forms
of Bryozoa.
But in the cretaceous formation of England, no coral-reefs are
observable; the zoophytal remains, with but a few local exceptions,
occur promiscuously intermingled with the fishes, shells, Radiaria, and
other marine exuviæ; although many layers, or thin seams of chalk and
marl, are largely composed of the detritus of corals, like the modern
deposits of the Bermudas (_Wond._ p. 613). These phenomena are in
accordance with the lithological characters of the White Chalk strata,
and the nature of its mollusca, both of which indicate a deep sea; and
coral-reefs are only formed at moderate depths. But in regions where
the sea was shallow, during the deposition of the cretaceous rocks,
beds of coral limestone were produced; and these also contain littoral
(sea-shore) shells, associated with the usual sponges and zoophytes
(_Wond._ p. 613).
In the marine secondary formations antecedent to the cretaceous,
namely, the Lias and Oolite, coral-reefs, which appear to have
undergone no change save that of elevation from the bottom of the sea,
and the consolidation of their materials by mineral infiltrations,
demonstrate a condition of the ocean in our latitudes, which is now
only met with in the tropics (_Wond._ p. 614).
The limestones of the Carboniferous, Devonian, and Silurian formations,
abound in anthozoan corals, and among them are many kinds of
Cyathophyllum, Lithododendra, Syringopora, Catenipora, Graptolites,
&c., which are characteristic of these deposits.
The Silurian zoophytes are figured in _Sil. Syst._; and the splendid
works on the British Palæozoic Fossils, by Prof. Sedgwick and Prof.
McCoy, now in course of publication, contain many admirable figures of
new, or but imperfectly known species.
The extensive beds of coralline limestones, which are found in the
Silurian strata, wherever they occur,--for the limestones of this
system in North America are characterized by the same species of corals
as those of England,--seem to indicate that a more equal temperature
prevailed throughout the ocean, at that geological epoch, than at the
present time, when the geographical distribution of the coral zoophytes
is strictly limited by temperature. The reef-forming genera are now
confined to waters where the temperature is not below 70°; their most
prolific development being 76°. The apparent exception, the occurrence
of coral-reefs at the Bermudas, is found to depend upon proximity to
the Gulf Stream (_Wond._ p. 614), which brings down the thermal waters
of the tropics, and increases the local temperature of the sea in
those localities.[259]
[259] Mr. Deane's splendid and masterly work on Corals, should be
studied by those who wish to be acquainted with the present state of
this branch of natural history.
[Sidenote: ON COLLECTING FOSSIL CORALS.]
On Collecting Fossil Corals.--Few instructions are required for the
collection of fossil zoophytes; for as the most important characters of
the several kinds have been pointed out in the previous descriptions,
the student will be able to select illustrative specimens for his
cabinet. The minute corals, &c. of the Chalk, and other limestones, are
to be obtained by the same process as that directed for the discovery
and preservation of the foraminifera, and other microscopic organisms,
at the end of the next chapter. The larger examples should be left
attached to a piece of chalk, when practicable, and the surrounding
stone removed with a knife or graver, so as to expose as much of the
fossil as may be required for the display of its characters, without
loosening its attachment to the block. When the investing chalk is
very hard, frequently pencilling the specimen with vinegar, or dilute
hydrochloric acid, will soften the stone, and render its removal easy,
by means of a soft brush: when acid is employed, the specimen must
afterwards be well rinsed in cold water.[260]
[260] It may be well to caution the collector against employing
sulphuric acid (commonly called _oil_ of _vitriol_) for this purpose,
for a white insoluble deposit (sulphate of lime) will thus be formed
on the specimen, and its appearance irremediably injured. Many of the
fossil corals obtained from the chalk of Dover Cliffs, are so saturated
with muriate of soda, from long exposure to the spray of the sea, as
to be liable to decomposition in the course of a few weeks, and are
therefore not worth purchasing of the dealers.
The zoophytes that are in part flint, and part chalk, as the
Ventriculites, (_ante_, p. 244, _Lign. 81_,) can rarely be obtained,
except through the quarrymen who have been instructed how to extract
them from the rock. The first specimen of this kind that came under
my notice, I discovered while breaking a mass of chalk, in search
of fungiform flints; when, to my great delight, I found the fossil,
_Lign. 81, fig. 3_, by which at once, and for the first time, was
shown the connexion between the chalk specimens, _Lign. 8, figs. 1,
2_, and the flints figured in _Lign. 8, figs. 2, 3, 6, 7, 8_. Upon
showing this fossil to the quarrymen, and exciting their attention by
suitable rewards, I obtained the illustrative series now in the British
Museum.[261] Much light would be thrown on the nature of other zoophytes
of the chalk that are invested with flint, if due care were taken in
the collection of specimens, and they were examined before extracted
from the rock. Loose, delicate specimens, whether from the chalk or
tertiary strata, should be affixed with strong gum-water to cards, or
pieces of thin board, covered with coloured paper.
[261] Petrifactions, Room VI. p. 466.
The Greensand Spongites, Siphoniæ, &c. may often be extracted from the
rock tolerably perfect, by a well-directed blow of the hammer; but
fragile species should be left attached to a block, and the surrounding
stone be carefully chiselled away, so as to expose the most essential
characters.
The Faringdon zoophytes are, for the most part, encrusted by an
aggregation of minute polyparia, shells, and detritus, which may be
partially removed by washing with a stiff brush, and their cavities
cleared with a stout penknife, removing the extraneous matter by
_chipping_, not by scraping, or the surface will be injured. In this
manner the beautiful specimens figured, _ante_, p. 228, were developed.
The Corals in the hard limestones can seldom be chiselled out to
advantage; for the most part, polished sections best exhibit the form
and structure of the originals.
Weather-worn or water-worn masses of coral limestone often display
the structure of the zoophytes of which they are in a great measure
composed, in a beautiful state of sculpture and relief: the silicified
or calcified corals appearing as perfect as if fresh from the sea.
The mural rocks of coral limestone at Florence Court, the seat of the
Earl of Enniskillen, are in many parts encrusted, as it were, with
syringopora and other tubular corals, laid bare uninjured by the long
and insensible effect of atmospheric erosion. A beautiful illustration
of the old aphorism,--"Aqua cavat lapidem non vi sed sæpe cadendo,"--is
afforded by the splendid examples of cateniporæ, fungiæ, caryophillæ,
sculptured in alto-relievo on the face of the Silurian rocks over which
dash the rapids at the Falls of the Ohio.
The silicified zoophytes of the West Indies, and those from Ava and the
Sub-Himalayas, form beautiful subjects for the microscope; and chips,
or sections, should be prepared in the manner recommended for fossil
wood in the same state of mineralization.
[Sidenote: LOCALITIES OF FOSSIL ZOOPHYTES.]
British localities.--The gravels and sands of the Crag afford most
favourable sites for obtaining tertiary zoophytes.
In the London clay at Bracklesham Bay, a species of Astrea (_A.
Websteri_) is often met with attached to flints and pebbles.
In the Greensand of Atherfield, in the Isle of Wight, an elegant coral
(_Astrea elegans_) is by no means rare.
The Greensand gravel-pits, near Faringdon, in Berkshire, abound, as
already mentioned, (_ante_, p. 228,) in many kinds of sponges, and
other porifera; and the quarries of oolitic limestone in the vicinity
of that town, yield the usual corals of the Jurassic formation in great
profusion, I know of no locality richer in fossil zoophytes, than
Faringdon.[262]
[262] See Excursion, Part IV. of this work.
The quarries of that division of the Oolite called Coral-rag (as in the
north-west of Berkshire, Oxfordshire, Gloucestershire, &c.), afford the
usual corals of the Oolite.
The Oolite near Bath contains many species, and large masses of a
minute coral (_Eunomia radiata_), are abundant.
At Steeple Ashton, in Wiltshire, numerous oolitic corals may be
obtained. The silicified _Astreæ_, of Tisbury, in the same county,
deserve particular notice (_ante_, p. 263).
Clifton, near Bristol, and Torquay and Babbicombe, on the Devonshire
coast, are celebrated for their coralline marbles and pebbles; and many
of the Derbyshire limestones are equally prolific in similar remains.
The Devonian marbles are so largely employed for ornamental purposes,--
as brooches, tables, and side-boards,--that the figures produced by the
sections of the enclosed corals must be familiar to the reader.[263]
[263] Specimens of these fossil corals, either as objects of natural
history, or as ornaments, may be obtained of Mr. Tennant, 149, Strand.
Dudley, Wenlock, and Ludlow, are well known for the abundance and
variety of Silurian polyparia.
Other localities of British corals have been mentioned in the course of
this review of fossil zoophytes.