Occasionally the soft body of the mollusk completely silicified—that is, transmuted into flint—is found in its natural position in the shell. A beautiful example of this kind is represented in Lign. 20. It is an extinct species of oyster: both valves were entire when I removed the chalk and cleared the specimen; part of one valve has been broken away to expose the petrified body of the animal. I have seen a Trigonia[AB] from the oolite of Tisbury in Wiltshire, in which the entire body of the mollusk was transformed into flint, and the branchiæ or lamellated gills were beautifully defined, though converted into semi-transparent chalcedony.

Note II. Page 17. Wood in Flint.

I would remind the reader that the white chalk, together with the various strata of sand, clay, and limestone, comprising the cretaceous formation of England, must be regarded as an ancient ocean-bed; in other words, an accumulation of earthy sediments, formed in the profound depths of the sea, in periods of long duration and of incalculable antiquity, and more or less consolidated by subsequent chemical and mechanical agency. These deposits are made up of organic and inorganic materials: the former consist of the debris of the cliffs and shores which encompassed the ancient ocean, of the spoils of the land brought into the waters by floods and rivers, and of mineral matter thrown down from chemical solutions. The organic substances are the durable remains of the animals and plants which lived and died in the sea, and of terrestrial and fluviatile species that were transported from islands or continents by rivers and their tributaries. The whole constitutes such an assemblage of strata as would probably be presented to observation, if a mass of the bed of the Atlantic 2,000 feet in thickness, were elevated above the waters, and became dry land; the only essential difference would be in the generic and specific characters of the imbedded animal and vegetable remains.

The vestiges of terrestrial and fluviatile animals and plants found in the chalk are comparatively but few: I have collected from Kent and Sussex, bones of gigantic land lizards, (the Iguanodon), of flying reptiles, (Pterodactyles), and of fresh-water Turtles, and water-worn fragments of stems of coniferous trees allied to the Araucaria or Norfolk Island Pine; fruits or aments of coniferse; and stems and foliage of plants related to the Cycas and Zamia.

A fragment of silicified wood imbedded in a flint, is represented in 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.>

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.

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.

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.

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]

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]

Note V. Page 27. 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]

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]

Note VI. Page 38. Rotaliæ in Chalk and Flint.

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.

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.

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.

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]

Note VII. Page 43. 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.

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.

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]

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]

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.

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]

The flints, figs. 3, 7, 8, 9, Lign. 25, were evidently formed in the manner exemplified in fig. 3, Lign. 26; figs. 2, 4, 6, are illustrated by fig. 4, Lign. 26; for the chalk specimens, Lign. 26, shew that all these flints have been moulded around Ventriculites, and that their diversity of figure has arisen from the quantity of silex that happened to permeate the substance of the zoophyte; if but a small portion, flint like figs. 2 and 4, were the result; if the quantity were considerable, the larger fungiform examples were produced.

Note IX. Page 50. Minute Corals from Chalk.

Some layers of chalk are composed of an aggregation of many kinds of delicate corals, the interstices being filled up with Rotaliæ and other foraminiferous shells. In the cliffs near Dover there are several beds of this nature, well known to collectors for the profusion of exquisite specimens they yield to the experienced investigator. Lign. 17, p. 50, represents several varieties from different localities; the small figures shew the natural size, and the enlarged ones their appearance when magnified. Attached to the surface of shells, and sometimes standing erect in crannies of flint nodules, beautiful corals may often be detected by the aid of a lens of moderate power. By brushing chalk in water, and examining the deposit, delicate fossils of this kind may also be obtained.[AR]

From the close analogy of the fossil corals to existing forms, it would not be difficult to give restored figures of the originals. Every little branch might be represented fraught with living polypes: in some cells the agile inmates might be shown with the mouth expanded, and the tentacula in rapid motion; in others withdrawn into their stony recesses, and devouring the infinitesimal atoms that constitute their food: even their varied hues might be introduced, and thus a vivid picture be presented of the microscopic beings which peopled the waters of the ancient chalk ocean.

That the Corals, which from their elegance and beauty are preserved in almost every cabinet, have been fabricated—or, in other words, built up—by polypes, in the same manner as the honey-comb of the bee and wasp, is so prevalent yet erroneous an opinion, that I am induced to point out its fallacy, by giving a brief account of the formation of these substances. The three recent specimens represented in Lign. 27 will serve to illustrate my remarks.

The coral, fig. 1, was an internal axis or skeleton, deposited by the soft fleshy integument with which, when living, it was wholly invested; in the same manner as are the bones of animals, by the special membrane (periosteum) that secretes them. This integument lined every cell, and the polypes were permanently united to it. When the live coral is taken out of the water, the animalcules shrink up and quickly perish; their soft parts and the external investing substance putrefy, and the stony axis beset with the radiated cells alone remains.

In the example of Oculina ramea, or May-blossom Coral, fig. 1, from the Mediterranean, the cells are large and distinct; in the Madrepore from the West Indies, fig. 2, they are small and very closely aggregated.

The specimen of Isis (fig. 3) belongs to a group of coral-zoophytes in which the polype-cells consist of a substance that is durable, but not so hard as coral, and invests an axis composed of a tough flexible material, which is exposed at the base of fig 3, by the removal of the external or cortical part in which the polypes were situated. The Gorgonia, or Venus's fan, has a similar structure and composition.[AS]