_Lign. 21_. It was obtained from a wall in Lewes Priory in Sussex; and
though it has been exposed to the atmosphere seven or eight centuries,
still exhibits the characteristic internal structure.
Note III. Page 20. _Whitby Ammonites._
[Sidenote: AMMONITES.]
[Illustration: _Lign. 22_:--Ammonites from the cretaceous formation.
1. _Ammonites varians_, from Hamsey.
2. _A. Dufresnoyi_: 2_a_, part of the same.
3. _A. lautus_: 3_a_, keel and septum of the same.
]
The Ammonites differ from the Nautili in having the margins of the
septa or internal shelly partitions (which in the latter are smooth),
foliated or wrinkled; and the siphunculus or tube placed along the
back of the shell, whereas in the Nautilus it is central. The sides of
the shell in the Ammonites are very generally more or less ornamented
with arched elevations and depressions, and studded with spines and
tubercles, as in the specimens above figured.
There are several kinds of Ammonites found in the Lias at Whitby and
other places in Yorkshire; the most common species is figured in
_Lign. 7_. p. 20; the dark colour of this fossil is produced by the
argillaceous stone with which it is now filled. The internal structure
of these Ammonites is generally well preserved, the chambers being
lined with spar or other mineral matter; transverse polished sections
are often very beautiful from the several cells being occupied by
variously coloured marble, susceptible of a high polish. (Pl. III.) In
some examples the entire shell is transmuted into brilliant pyrites
(sulphuret of iron), and the chambers are filled with white spar; a
specimen of this kind in my possession, collected by Lady Murchison, is
the most elegant fossil imaginable.
[Illustration: _Plate III._
_Polished section of an Ammonite._
_Page 70._]
[Sidenote: AMMONITE-MARBLE.]
It is not unusual for the visitors at Whitby to inquire of the
collectors how it is that the head of the animal is never found?
and the crafty dealers, willing to accommodate the taste of their
customers, carve the extremity of an Ammonite into the semblance of
a serpent's head, and affix two red eyes; thus producing a veritable
proof of the truth of the legend of St. Hilda! My young readers will
not be duped by this trick-of-trade, if they reflect but a moment on
the real nature of a fossil Ammonite: they will remember that it is a
shell which, when empty, became filled with what was then soft mud, but
is now stone; in like manner as if liquid plaster of Paris were poured
into an empty snail-shell and consolidated.
In some parts of Somersetshire, a beautiful marble composed of an
aggregation of two or three small species of Ammonites, is used for
sideboards and other ornamental purposes: the polished slabs are
diversified by the numerous sections of the shells.
Some of the clays of the Lias abound in a species of Ammonite of
extraordinary beauty from the iridescent lustre of the pearly coat of
the shell: a slab of stone from Watchett, on which a hundred or more
Ammonites of this kind are displayed, may be seen in the British Museum.
Note IV. Page 23. _Fossil Nautili._
The beauty, elegant form, and remarkable internal structure of the
shell of the Nautilus, have rendered it in all ages an object of
curiosity and admiration: yet an accurate knowledge of the organization
of the animal to which it belongs, has but recently been obtained. The
Nautili may be regarded as Cuttle-fish or _Sepiæ_, inhabiting shells
furnished with an apparatus to impart buoyancy, and enable the animals
to swim on the surface, or sink to the profound depths of the ocean.
A few explanatory remarks on the nature of the recent Sepia may be
necessary to render the subject intelligible to the unscientific reader.
[Sidenote: RECENT NAUTILUS.]
The _Sepia_ or Cuttle-fish of our seas is of an oblong form, and
composed of a soft substance covered with a tough integument or skin:
it varies from a few inches to a foot or more in length. The mouth
is placed in the centre of one extremity of the body, and has a
pair of powerful, curved, horny mandibles, much resembling the beaks
of a parrot: it is surrounded by eight long arms like the rays of a
star-fish, and these are beset with rows of little cups which act as
suckers, and enable the animal to secure its prey, and attach itself
with great firmness to any object.[AC] It has a distinct head, with
two eyes as perfect as in the vertebrated animals, and complicated
organs of hearing: and below the head there is a tube or funnel which
acts as a locomotive instrument, and propels the animal backwards by
the forcible ejection of the water which has served the purpose of
respiration, and can be thrown out with considerable force by the
contraction of the body. The soft parts are supported by a large
internal bone or osselet of a very curious structure, which, when dried
and reduced to powder, forms the substance used by scriveners, termed
_pounce_. These naked mollusca also possess a membranous bag or sac,
containing a dark-coloured fluid resembling ink in appearance, which
they eject into the surrounding water upon the approach of danger, and
by the obscurity thus induced foil the pursuit of their enemies. This
fluid, when inspissated, forms the base of the colour termed _sepia_ by
artists.
[AC] From this arrangement of the organs of prehension around the head,
this order of mollusca is termed the _Cephalopoda_; _i. e._, the feet
around the head.
The body of the Nautilus resembles in its essential characters that of
the Cuttle-fish, and occupies the large outer receptacle of the shell;
maintaining a connection with the inner compartments by means of the
membranous siphunculus or tube, which is only partially invested with
shell. The internal chambers are air-cells, and the animal can fill
the siphunculus with fluid, or exhaust it at will; the difference thus
effected in its specific gravity enables it to rise to the surface or
sink to the bottom with facility. Now if' we imagine a Cuttle-fish
placed in the outer chamber of a Nautilus-shell, and provided with a
siphuncule, but having neither ink-bag nor osselet--these organs being
unnecessary to an animal possessing a chambered shell--we shall have a
general idea of the nature of the recent species.
The Nautilus is essentially an inhabitant of deep water: it creeps
along the ground at the bottom of the sea, with its shell upwards like
the snail; and by means of its arms can proceed with considerable
speed.[AD]
[AD] See '_Conchologia Systematica_,' vol. ii. p. 302, and '_Elements
of Conchology_,' p. 22, by Mr. Lovell Reeve, F.L.S., for an admirable
description of the recent Nautilus, with illustrations.
A large and splendid species of fossil Nautilus is not uncommon in the
London Clay of the Isle of Sheppey, Sussex, and Hampshire. The chambers
are often lined with spar or other brilliant mineral matter; and
polished sections, like those of the Ammonites, admirably display the
internal structure.[AE]
[AE] See Dr. Buckland's '_Bridgewater Treatise_' for numerous figures
of Ammonites and Nautili; _plates_ 31 to 34. Consult also '_Medals of
Creation_,' vol. ii. p. 457.
Note V. Page 27. _Brighton Cliffs._
[Sidenote: BRIGHTON CLIFFS.]
The stranger who approaches Brighton by the railroads through deep
tunnels and cuttings in the chalk, and perceives the town spread
over the plain and on the sides of a valley of the South Downs, will
naturally expect to find the sea-shore bounded by chalk-cliffs. But
a wall of admirable construction, extends from the Steyne to beyond
Kemptown, and effectually conceals from view the materials that
compose the site of that part of Brighton; a ramble along the shore to
Rottingdean is therefore necessary to reveal to the inquiring observer,
the nature of the strata that flank the southern border of the Downs.
The sketch given in page 27, represents the appearance of part of the
coast to the east of Kemptown. The base of the cliff to the height of a
few feet, is seen to consist of the white chalk with its usual layers
of flint nodules, forming a low wall or terrace, which slopes seaward,
and extends far into the British channel--probably to the opposite
coast of France: at low-water a considerable expanse of modern shingle
and sand is spread over, and in a great measure conceals, the chalk,
at a few yards distance from the cliff. Upon the terrace of chalk, at
the height of from ten to fifteen feet above the modern beach, there
is a bed of pebbles and sand, containing also a considerable number
of boulders of granite, porphyry, and other crystalline rocks foreign
to the south-east of England: in fact, a sea-beach, which must have
been formed at some remote period, in the same manner as the modern
shingle. Upon this ancient beach are strata of loam, and chalk-rubble,
with flints partially water-worn, and boulders of sandstone, breccia,
granite, &c., constituting the upper sixty or eighty feet of the cliff.
In these beds, and also in the ancient shingle, many teeth and bones of
mammoths (extinct species of elephant), horse, deer, oxen, and other
ruminants, and bones of whales, have been discovered.[AF]
[AF] See '_Medals of Creation_,' p. 914.
[Sidenote: THE SUSSEX COAST.]
A few hundred yards beyond Kemptown the inroads of the sea have
destroyed all vestiges of the strata above described, and the cliffs
consist of a perpendicular wall of chalk; if we extend our walk to
Rottingdean, we shall perceive here and there isolated patches of the
ancient shingle, and of the calcareous strata containing elephants'
bones.
The appearances described demonstrate the following changes in this
part of the Sussex coast. _Firstly_, the chalk terrace (_Lign. 9, c_;
p. 27) on which the ancient shingle (_b_) rests, was on a level with
the sea for a long period; for this beach must have been accumulated,
like the modern, by the action of the waves on the then existing chalk
cliffs. But there must also have been some cause not now in operation,
by which pebbles, and boulders of granite and other rocks foreign to
this coast, with bones of extinct mammalia, &c., were thrown up on
the strand, and imbedded in the beach then in progress of formation.
These materials were probably brought from some distant part of the
then continental shores by floating ice: an agency by which delicate
bones and shells may be transported and deposited without injury amidst
pebbles and boulders.
_Secondly._ The whole line of coast with the ancient shingle must
have subsided to such a depth as to admit of the deposition of the
calcareous materials forming the "Elephant bed;" and from the absence
of beach and shingle in these strata, it may be inferred that this
deposition took place in tranquil water: possibly at that period this
part of the Sussex coast formed a sheltered bay.
_Lastly._ The land was elevated to its present level, and the formation
of the modern sea-beach and cliffs commenced.[AG]
[AG] See '_Medals of Creation_,' "On the Geological structure of
Brighton Cliffs," p. 913.
Note VI. Page 38. _Rotaliæ in Chalk and Flint._
[Sidenote: FOSSIL FORAMINIFERA.]
The shells called _Rotaliæ_ (see _Lign._ 5 and 6, p. 14 and 16) belong
to a group of marine animals of very simple organization, and which
present great variety in the form and markings of their testaceous
coverings; but they all agree in having the sides of the shell pierced
by numerous holes or foramina; whence the scientific term of the
Order, _Foraminifera_, is derived: these openings are for the egress
of delicate filaments, which appear to be organs of progression and
respiration.
The _Foraminifera_ are, with but few exceptions, exceedingly minute;
in an ounce of sea-sand, between three and four millions have been
detected. The body of these animalcules consists of uniform granules
enclosed in a skin or integument, having one or more digestive sacs
or cavities; these creatures appear, in fact, to be mere polypes,
protected by testaceous coverings. Some have but a single cell; others
have many, disposed in a conical or cylindrical form; many kinds, of
which the _Rotaliæ_ are examples, are discoidal involutes, and divided
internally by septa into distinct chambers:[AH] they resemble in this
respect the shell of the Nautilus, but are readily distinguished by the
perforations.
[AH] See '_Wonders of Geology_,' 6th Edit. p. 322.
All the various kinds of _Foraminifera_ swarm in the present seas,
and were not less numerous in the ancient ocean. We have seen that
the white chalk almost wholly consists of a few genera of these
animalcules; and in many strata of sand they are so abundant, that
a cubic inch of the mass contains upwards of sixty thousand. In the
_Rotalia_, the body is entirely enclosed within the shell, and occupies
all the cells; and long, soft, tentacula are sent off through the
foramina. The shell, therefore, though resembling in form that of
the Nautilus, is essentially different; for in the latter, the outer
chamber only is occupied by the body of the animal, the internal ones
being successively quitted empty dwellings; whereas, in the _Rotaliæ_
and analogous _Polythalamia_,[AI] all the cells are contemporaneously
filled by the soft parts of the animalcule.
[AI] _Polythalamia, many-chambered_, is a general term applied to these
shells.
[Sidenote: RECENT FORAMINIFERA.]
When the shell is removed, which is readily effected by immersion in
diluted hydrochloric acid, the body is exposed, and found to consist
of a series of lobes or sacs, united by a tube corresponding somewhat
in its position with the siphuncle of the Nautilus, but which is the
digestive canal. The body of a recent animalcule of this kind, deprived
of the shell, is figured in _Lign. 23_.
[Illustration: Lign. 23:--The body of a recent animalcule
allied to the _Rotalia_, deprived of its shell; _highly magnified_.]
Not only the characters of fossil shells of such infinite minuteness
can be revealed by the microscope, but even the soft parts of the
animalcules which inhabited them; for these are occasionally preserved,
and may be demonstrated with as much distinctness as the recent
examples.[AJ] In flint the soft parts of _Rotaliæ_, _Textulariæ_,
&c., are abundant, and may be seen, with but little preparation, like
insects in amber: the specimen figured in _Lign. 12_, p. 39, shews
the body of a _Rotalia_ well defined; the only preparation this atom
of flint has undergone, is immersion in Canada balsam. To detect such
delicate structures in chalk requires, however, some experience in
microscopic manipulation, as the calcareous matter must be dissolved
in hydrochloric acid, and the animal substance separated from the
residuum.[AK]
[AJ] See '_Wonders of Geology_,' 6th Edit., p. 322.
[AK] See my '_Memoir on the fossil remains of the soft parts of
Foraminifera in Chalk, &c._' Philosophical Transactions, 1846, p. 465.
Note VII. Page 43. _Isle of Wight Pebbles._
[Sidenote: ISLE OF WIGHT PEBBLES.]
The nodules and veins of flint that are so abundant in the upper
chalk, have probably been produced by the agency of heated waters
and vapours; the perfect fluidity of the siliceous matter before its
consolidation is proved, not only by the sharp moulds and impressions
of shells and other organisms retained by the flints, but also by the
presence of numerous remains in the substance of the nodules, and the
silicified condition of the sponges and other zoophytes which abound in
the cretaceous strata.
Now although silex, or the earth of flint, is but sparingly soluble in
water of the ordinary temperature, its solution readily takes places
in vapour heated a little above that of fused cast iron, as has been
proved by direct experiment;[AL] and similar effects are being produced
at the present moment by natural causes. The siliceous deposits thrown
down by the intermittent boiling fountains, called the Geysers, in
Iceland, are well known;[AM] and in New Zealand this phenomenon is
exhibited on a still grander scale. From the crater of the volcanic
mountain of Tongariro,[AN] which is several thousand feet above the
level of the sea, jets of vapour and streams of boiling water highly
charged with silex, are continually issuing forth, and dashing down
the flanks of the volcano in cascades and torrents, empty themselves
into the lakes at its base. As the water cools, siliceous sinter is
deposited in vast sheets, and incrustations of flint form around the
extraneous substances lying in the course of the thermal streams. Silex
is also precipitated by the boiling waters in stalagmitic concretions,
and in nodules resembling in colour and solidity the flints of the
English chalk. The complete impregnation and silicification of
organized bodies is attributable to an agency of this kind; and
although the origin of the siliceous waters that deposited the nodules
and veins of flint in the chalk is still involved in obscurity, the
mode in which the latter were formed is satisfactorily elucidated.
[AL] See '_Wonders of Geology_,' p. 100.
[AM] Ibid., p. 95.
[AN] Ibid., p. 98.
[Illustration: Lign. 24:--Zoophytes in Chalk and Flint.
1. A minute coral from chalk and flint; the lower figure is of the
natural size.
2. Branch of a sponge in flint. 3. Pebble enclosing a zoophyte.
]
Of the perfect transmutation into flint of the most delicate organic
structures, the pebbles strewn along the sea-shore of the south coast
of England, afford a beautiful illustration; those from the Isle of
Wight are especially celebrated for their rich and varied colours.
The most common and interesting are those which exhibit sections of
Choanites, as in the specimen which suggested the reflections embodied
in these pages. Other allied forms are scarcely less beautiful; the
petrified zoophytes called _Siphonia_, which, when living, consisted
of a soft mass traversed by tubes, for the free ingress and egress of
the water, often display the internal structure of the original: as
in the polished transverse section figured above, _Lign. 24, fig. 3_.
Other bodies of this class occur in the flint, and present interesting
examples of the zoophytes of the chalk ocean.
But many of the Isle of Wight pebbles exhibit no traces of animal
structure, yet are valuable and instructive as mineralogical specimens:
such are the clear and transparent pebbles with bands and veins of
quartz and chalcedony. Some specimens are as pellucid as rock-crystal;
others are of a bright yellow, amber, dark-brown, and bluish-black
colour, and are often mottled with dendritical or arborescent
manganese. (_Plate IV._) The moss agates, as they are called by the
lapidaries, are silicified sponges. Small pebbles of pure transparent
rock-crystal are often found among the shingle in Compton and Sandown
bays, and have probably been washed out of the wealden strata; for
similar stones occur in the Tilgate grit, and at Tunbridge Wells: in
the latter place, they are cut and polished for rings, brooches, &c.
[Illustration: _Plate IV._
_Polished sections of Pebbles._
_Page 86._]
[Sidenote: ZOOPHYTES OF THE CHALK.]
On the shores of the Isle of Wight, pebbles of jasper, resembling those
from Egypt, and of banded quartz, with arborescent markings, or with
zones of rich brown, are also met with; these do not appear to have
originated from the chalk strata.
Pebbles of silicified wood have been collected in Sandown bay by Mr.
Fowlstone; and water-worn boulders and pebbles of petrified wood,
bones, &c., are common in Brook bay; rolled masses of the fresh-water
shelly limestones (Sussex and Purbeck marbles) are also abundant in the
same localities.[AO]
[AO] All these varieties may be obtained of Mr. Fowlstone, 4, Victoria
Arcade, Ryde.
Note VIII. Page 45. _Zoophytes of the Chalk._
Zoophytes, especially sponges, occur in such prodigious numbers in some
of the chalk strata, that the nucleus of almost every flint nodule is
an organic body. In many instances the silex has completely permeated
the animal substance, as in the pebbles before described; but sometimes
the sponge is a white calcareous mass, occupying a hollow in the flint:
a branched specimen of this kind, exposed on breaking a small nodule,
is represented at _Lign. 24, fig. 2_.
In describing sponge as an animal substance, it may be necessary to
explain that the sponge in ordinary use is the flexible skeleton of
a living zoophyte, and was originally invested with a gelatinous or
slimy matter, which lined all the pores and channels. When alive in
the water, currents constantly enter the outer pores, traverse all
the internal inosculating canals, and issue from the larger orifices
which often project above the surface in perforated papillæ. By
the circulation of the sea-water through the porous structure, the
nutrition of the animated mass is effected; and the modifications
observable in the number, size, form, and arrangement of the pores,
canals, and apertures, in the different kinds of this type of
organization, are subservient to this especial function.
But associated with the true _Poriferæ_ or sponges, are numerous
zoophytes which resemble them in form, but are of an entirely distinct
nature; for they are the fossilized remains of _Polyparia_, that is, of
the frame-work of an aggregation of polypes, each individual of which
had an independent existence, although the whole were united by one
common living integument, like the _Alcyonium_, or dead-men's fingers,
of our coasts.[AP]
[AP] See '_Medals of Creation_,' p. 251.
[Illustration: Lign. 25:--Flints deriving their forms from the
zoophytes they enclose.]
[Sidenote: FUNGIFORM FLINTS.]
Among the flints whose forms depend on the organic bodies they enclose,
are some which bear so close a resemblance in shape to _Fungi_, that
they are provincially called in Sussex "_petrified mushrooms_;" several
of them are figured above (_Lign. 25_). In these fossils there are
openings at the base, and a groove on the margin of the upper part, in
which the structure of the enclosed body is generally more or less
distinctly seen; and upon breaking one of these bodies, a section of
a funnel-shaped zoophyte is obtained. The origin of these flints will
be understood by reference to the four interesting specimens here
delineated, one-sixth of the natural size in linear dimensions.
[Illustration: Lign. 26:--Ventriculites from the Chalk, Lewes.
1. A perfect specimen in Chalk, shewing the external net-like surface.
2. An expanded specimen, displaying the inner surface studded with cells.
3. A Ventriculite with the lower part enveloped in Flint.
4. Part of a Ventriculite; the base invested with Flint: the root-like
fibres are seen at a.
]
[Sidenote: VENTRICULITES.]
This zoophyte, to which the name of _Ventriculite_ has been given to
denote its usual shape, was a hollow inverted cone, terminating at
the base in a point, whence radicles or root-like processes were sent
off, by which the animal was firmly attached to the rock. The outer
integument was disposed in meshes like a net (see _Lign. 26, fig.
1_), and the inner surface was beset with regular circular openings,
the orifices of tubular cells (_fig. 2_); each of which was probably
occupied by a polype. The substance of the _Polyparium_, or general
support of this family of animalcules, which alone occurs in a fossil
state, appears to have been analogous to that of the soft _Alcyonia_,
and to have possessed a common irritability; the entire mass
contracting and expanding, as is the case in many recent zoophytes.[AQ]
[AQ] See '_Wonders of Geology_,' 6th Ed., p. 610; '_Medals of
Creation_,' p. 273-276; and '_Geological Excursions round the Isle of
Wight_,' pp. 179-184, for an account of the silicification of these and
other Zoophytes.