Chapter 28

Lign. 151. Nautilus elegans.Lower Chalk.Lewes.(1/6nat. size.)

In the White Chalk near Lewes, casts of several very large Nautili have been found; but shells of this genus aremore abundant in the lower division, theChalk-marl. A large and beautiful species,Nautilus elegans(Min. Conch.tab. 116), is not unusual in the marl-pits near Lewes, Clayton, Steyning, &c. and may be considered as characteristic of that portion of the Cretaceous deposits. The first specimen discovered (Foss. South D.tab. xx) was from the marl-bank immediately at the foot of the mound on which stands the church ofHamsey, a little hamlet on the north of Lewes; a spot from which I obtained numerous other cephalopodous shells, at that time unknown as British species. The collocation of fossils at Hamsey is similar to that observable in the quarries at St. Catherine’s Mount, near Rouen. These remains only occur as casts, no vestige of the shell remaining; but sections will sometimes show the situation of the siphon, its tube being filled with a different material from that which occupies the cells. This is exemplified in the section of a smaller species (N. pseudo-elegans,Lign.150,fig.2), in which the channel of thesiphon is filled with a dark-coloured marl,a; the lines formed by the section of the smooth septa are also shown. In the same lignograph,fig.3, a front view and profile of another chalk-marl Nautilite are figured.[411]

[411]The student will find a section of the shell of the recent Nautilus a very instructive object of comparison, in the investigation of the fossils of this family.

Lign. 152. Nautilus Saxbyi.Lower Greensand.

In the Chalk, as well as in many other calcareous deposits, the shells of the Nautili, Ammonites, &c. are very rarely preserved; even the internal septa are often dissolved, and the stony casts, moulded in the cells, remaindistinct, and readily separate (Lign.153). An entire series, from the innermost cell to the outer chamber, may sometimes be obtained (in the Coralline Oolite); forming, as it were, a dissected model of the internal structure.[412]The beaks or mandibles are occasionally found fossil (Lign.150,fig.1).

[412]Bd.pl. xlii.fig.1: see also plates xxxi. to xliii., for illustrations of Nautilites.

Lign. 153. Casts of chambers of Nautilus and Ammonite.(1/2nat.)Fig.1.—Cast in calcareous spar of a chamber ofNautilus.From the London Clay.2.—Cast of a chamber ofAmmonites excavatus.From the Coral Rag.

Lign. 154. Clymenia:1/2nat.Devonian.Fig.1.—Clymenia Sedgwickii.2.—Front view of the same.3.—Vertical section ofC. striata, showing the siphunculus on the inner edge of each septum.4.—Suture ofC. striata.

Clymenia(Lign.154,Ly.fig.406).—This genus belongs to the Nautilidæ, and is peculiar to the Devonian deposits.It differs from the allied genera in the siphuncle being situated on the inner margin of the septa. The shell is discoidal, and the septa are very slightly lobed. At Elbersreuth, near Bareuth, in the N. E. of Bavaria, the Devonian strata abound in these shells; thirty-five species have been found, the greater number being peculiar to that locality.

In England they are chiefly found at South Petherwin, Cornwall, and in the Devonshire marbles. (See Phillip’s Pal. Foss. Devonshire.)

ORTHOCERAS.

Orthoceras(straight shell),Lign.155.—The shells of this genus may be described as Nautili uncoiled and extended in a straight line. They are straight, elongated, chambered shells, with smooth and gently undulated septa, which are concave towards the opening or upper part, and have the siphuncle either central, or not far removed from the centre. TheOrthoceratitesmore especially belong to the ancient Secondary strata. They first appear in the Silurian, and abound in the Devonian and Carboniferous. They vary in size from a few inches to several feet in length, and eight or nine inches in diameter; and in form, from a slender elongated cone, to a short, massy, almost spherical figure, with a contracted orifice. Some examples have been noticed with upwards of sixty cells. Mr. Sowerby figures and describesO. giganteum(Min. Conch.tab. 246), from Scotland, as exceeding seven or eight feet in length; and I discovered on the beach at Brighton, where it had probably been brought by some vessel, among ballast, a fine fragment of the same species, indicating as great a magnitude. Several species are figured,Lign.155, to show the structure and appearance of these fossils. The casts of the separate cells are often found. The section,fig.3, from the red marble of Devonshire, beautifully displays the situation of the siphuncle, and the lines of the septa. The shelly siphuncle, which is moniliform (bead-like), or dilated at eachchamber, is replaced by white spar; and the membranous internal tube is filled with a dark substance, probably molluskite.

Lign. 155. Orthoceratites.Fig.1.—Orthoceras striatum.(Min. Conch.)Devonian.2.—Orthoceras conicum.Whitby.Carboniferous.3.—Vertical section of anOrthoceras, showing the central siphon, and the chambers.Devonshire.4.—Orthoceras laterale.Carb.(Min. Conch.)5.—Orthoceras gregarium.(Munch. Sil. Syst.)a.One of the septa.b.A portion covered at the upper part by the shell.c.The lower part of the same specimen, displaying the septa.

Lign. 155. Orthoceratites.

There are some species in which the internal tube, as well as the external, is calcareous, and the two are connected at regular intervals, by radiating, hollow processes. TheseOrthoceratites have been principally obtained from the Silurian limestones, at Lake Huron; they also occur in Ireland. Mr. Stokes, who first investigated their structure, has arranged them in a distinct genus, with the name ofActinoceras(radiated-horn).[413]

[413]See Geol. Trans, second series, vol. v. p. 708.

Slabs of reddish Devonian limestone, containing Orthoceratites, may be seen in some of the pavements at Hampton Court, and in Chelsea College, which when wet present excellent sections of the enclosed shells.

Lign. 156. Ammonites from the Cretaceous Formation.

Ammonitidæ.—TheAmmonites, orCornua Ammonis(so called from a supposed resemblance to the horns engravenon the heads of Jupiter Ammon), are among the most common and well-known fossils of the British secondary strata. In some districts, as in Yorkshire and Somersetshire, where the Ammonites abundantly prevail, they were noticed in very remote times. Local legends, ascribing their origin to swarms of snakes turned into stone by the prayers of some patron saint, are still extant, and are perpetuated by the name of snake-stones, by which these fossils are provincially known. The Lias, near Whitby, in Yorkshire, contains immense numbers of two or three species, one of which (Am. bifrons) is figured inLign.127,fig.7, and another inLign.157.

Lign. 157. Ammonites communis.Lias.Whitby.

The shells comprehended in this family are either spiral, involute, arched, or straight; their septa are deeply lobed, and have the margins foliated. The siphuncle is dorsal, as shown by the notch in the cast,Lign.156,fig.3a. Several hundred species have been described; they are divided into genera which are characterized by essential modifications in the direction of the spire, and the inflections of the septa. Thus, in theAmmonites,Lign.156, the spire is involute, and all the turns contiguous; inCrioceras(curved-horn),Lign.160,fig.2, evolute; inScaphites, incurved at both extremities,Lign.162;Hamites, bent like a siphon, or hook,Lign.161,fig.1;Turrilites, spiral, round a vertical axis,Lign.163; and inBaculites, straight,Lign.161,fig.2. New genera are continually being added, to embrace modifications of structure which appear to be too important for specific distinctions. I will endeavour to render this arrangement more clear to the student by the following definitions.

A straight tube, or horn, of an elongated conical figure, tapering to a point, and having its cavity divided by transverse partitions, which septa are not straight, but undulated, and their edges, which fit into the walls of the tube, deeply wrinkled, and the whole series pierced by a pipe running along near the outer margin, would be the model of the shell termedBaculites,Lign.161,fig.2, (Bd.pl. xliv.fig.5;) which may be regarded as a straight Ammonite. A similar shell, gently arched or curved, would be aToxoceras,Lign.160,fig.1; the same tube, bent upon itself, like a siphon, into unequal limbs, not contiguous, aHamites,Lign.161(Bd.pl. xliv.fig.10); bent and approximate, or anchylosed in a straight line,Ptychoceras,Lign.161,fig.4; partially convoluted, the whorls contiguous, and the free end recurved,Scaphites,Lign.162; the same form, but the spire not contiguous,Ancyloceras,Lign.160,fig.3; spirally twisted around an axis,Turrilites,Lign.163(Bd.pl. xliv.fig.14); coiled, but the turns not touching each other,Crioceras,Lign.160,fig.2; lastly, coiled up in the form of a disk, all the turns being contiguous,Ammonites.

AMMONITE.

Ammonites.Lign.156, 157, 158.—Shell discoidal, more or less compressed, whorls of the spire contiguous, and often visible; septa lobed, their margins deeply sinuated; aperture symmetrical, border or lip thickened, often notched and auriculated. Siphuncle dorsal.

The student will be able readily to distinguish Ammonites from Nautili by attention to the above definition. The situation of the siphuncle, the foliated or wrinkled edges of the septa, as shown in the cast,Lign.156,fig.2; and when these characters are wanting, the arched ribs and elevations, as infigs.1 and 3, will serve as discriminating features. Like the fossil Nautili, the Ammonites most commonly occur as casts, the shell having been dissolved. Sometimes these consist of semi-transparent calcareous spar, the cast of each cell being distinct, but held together by the interlockingof the foliations of the septa; such examples are of great beauty and interest (seeBd.pl. xlii. figs. 2, 3); they most frequently occur in the limestones of the Oolite. The siphuncle is often preserved, even in the chalk specimens, in which all traces of the shell are lost. In a large Ammonite from, near Lewes, not only the shelly siphuncle remains, but even the internal membranous tube, converted into dark molluskite. Separate portions of similar siphuncles occur in the chalk, and have been mistaken for tubular shells.

Lign. 158. Ammonites Jason.1/2nat.Oxford Clay, Trowbridge, Wilts.a.—Lateral processes of the margins of the aperture

The outer lip, or margin of the aperture, is occasionally found entire. In some species there is a dorsal process, as in a very common Chalk Ammonite (A. varians,Lign.156,fig.1), which extends far beyond the margin; in other species, from the Oxford Clay, there are long, narrow, lateral appendages, (Lign.158). In the collection of S. P. Pratt, Esq., there is a small Ammonite, from the Inferior Oolite of Normandy, in which these processes meet over the aperture, leaving only a circular aperture towards the back of the shell (where the siphuncle of the animal would be situated) and a narrow fissure on the side next the involute spire. The specimen is unique, and can scarcely be regarded as a normal form.[414](Mr. Woodward.)

[414]M. Steenstrup has described a species ofPurpura, which at the close of its life shuts up the aperture of its shell, with the exception of the respiratory siphon.—Mr. Woodward.

From the small size of the cells of the Ammonites, particularly in those species which are of a depressed or flattened form, it was long doubted whether the outer chamber couldhave been sufficiently capacious to contain the body of the animal; and it was supposed that these shells were internal, like the recentSpirula, orCrosier. But Dr. Buckland has clearly demonstrated, that the outer cell of the Ammonite, if restricted in breadth, is sufficiently ample in length to have contained the soft parts of a Cephalopod, equal in magnitude to the largest known specimens, its proportion to the chambered part being as considerable as in the Nautilus. The outer chamber often occupies more than half, and in some instances the entire circumference of the outer whorl (seeBd.pl. xxxvi.).

In certain argillaceous deposits, as the Galt, and the clays of the Lias, Ammonites with the shell preserved are abundant; generally the outer opaque layer is wanting, or adheres to the matrix when a specimen is removed, leaving only the internal nacreous, or pearly coat. Folkstone, on the coast of Kent, is celebrated for examples of this kind, which may easily be collected from the Galt, which forms the base of the cliffs, at Eastware Bay. Watchett, in Somersetshire, is equally rich in the pearly Ammonites of the Lias; entire layers of these beautiful organic remains occur in the limestones and in the shale exposed at low water.[415]

[415]A splendid group of these Ammonites may be seen in the Gallery of Fossils at the British Museum.

The shell of the Ammonite is generally thinner and more delicate than that of the Nautilus. However thin these shells may be, they are possessed of great strength of structure. Not only is the shell one continuousarch, but it is moreover provided with transverse arches or corrugatedribs, which, like the flutings on metal pencil-cases, andcorrugated sheet-iron, greatly strengthen the thin material. These ribs are further subdivided, so as to multiply supports as the convexity of the shell enlarges, in a manner somewhat similar to thegroin-workof vaulted roofs. The spines, tubercles, and bosses, which often arise from the ribs, are somany additions to the strength of the latter. The sides of the shell are also supported by the transverse plates forming thesepta, or divisions of the chambers, and, as these plates are very sinuous where they meet the sides of the shell, they distribute their support over a considerable portion of the surface.[416]These complicated edges of theseptaform the delicate and intricate lines of foliation (sutures) seen on the casts of Ammonites (Lign.156,fig.2), Baculites (Lign.161,fig.3), Hamites, &c. In some species the shell is thick and dense, as in the Ammonites of the Kimmeridge Clay near Aylesbury, in which one species (Ammonites biplex,Min. Conch.pl. ccxciii.) in particular abounds, and is very generally invested with the shell, as perfect as if recent. The same Ammonite occurs in the Portland limestone above, in the state of casts, without any vestige of the shell. In some strata the shell is replaced by calcareous spar; in others by silex or flint.[417]In the pyritous clays and shales of the Lias, the shell and all its delicate internal mechanism are coated with or replaced by brilliant sulphuret of iron, forming the most exquisite natural electrotype imaginable. Polished vertical sections of these fossils often exhibit the inner cells filled with transparent white calcareous spar; sometimes with groups of crystals of sulphate of lime. The Ammonites of the Galt, and of the Kimmeridge Clay, are also frequently imbued with the same mineral.

[416]See Bd. i. p. 339, &c.[417]See an admirable figure of a chalcedonic specimen, exhibiting the foliated septa of an Ammonite,Bd.pl. xli.

[416]See Bd. i. p. 339, &c.

[417]See an admirable figure of a chalcedonic specimen, exhibiting the foliated septa of an Ammonite,Bd.pl. xli.

There are about two hundred identified species of Ammonite in the British strata, ranging through all the secondary formations; they have not been found in the Tertiary deposits. They vary in size from half an inch to four feet in diameter.[418]

[418]I have seen imprints of the large Chalk Ammonite,A. peramplus(Min. Conch. pl. ccclvii.), on the shore off Rottingdean, and Beachy Head, which indicated even larger proportions.

Certain species are restricted to particular formations, and are therefore oftentimes of essential aid in determining the relations of a deposit; for example, theGaltcontains several species not found in the upper division of the Chalk; and in the Chalk-maid are species that have not been discovered in other strata. Certain Ammonites of the Lias are peculiar to that formation (asA. Walcottii,Lign.127,fig.7, p. 397; andA. communis,Lign.157). Ammonites of species allied to those of our Middle and Lower Oolites have been discovered in strata in the Himalaya mountains, several thousand feet above the level of the sea.

Lign. 159. Goniatites.nat.Carb. Syst.

GONIATITES. CERATITES. CRIOCERAS.

Goniatites,Lign.159.—From the numerous family of Ammonites, a separation has been made of a large division,in which the margins of the septa are not deeply notched or foliated, and are destitute of lateral crenatures or denticulations, so that their outline always presents a continued uninterrupted line. The siphuncle is relatively small. The last or outer cell of the shell extends beyond one turn of the chambered part. The back is occasionally keeled, but in most species is round. In illustration of this genus, which is namedGoniatites, I have selected two common species (Lign.159) from the Carboniferous limestone, and annexed outlines of a suture (the edge of the septum) of a Goniatite, and of an Ammonite, for comparison. The importance of the separation of this type of Ammonites into a distinct genus, relates to the Goniatites being restricted to some of the older sedimentary strata; for although there are sixty British species, none of them have been observed above the Carboniferous system.[419]

[419]G. Henslowi,G. striatus, andG. sphæricus, are figured inBd.pl. xl.

InCeratitesthe sutures are more simple than in the Ammonite, being lobed rather than foliated; and the alternate lobes have their edge crenulated or finely toothed. (C. nodosus,Bd.pl. xl.) This genus is found in the Muschelkalk and the Keuper formations of Europe and Asia.

Our limits will not permit us to extend this notice of the very numerous family of Ammonitidæ,[420]except to offer a few illustrations of some of the modifications in form to which we have already alluded, and which will assist the student in discriminating these fossil remains.

[420]For further information, Dr. Buckland’s Treatise, and the respective articles in the Penny Cyclopædia, may be referred to. Mr. Woodward’s Manual should be consulted for the classification of the family, and M. D’Orbigny’s Paléontologie Française for the illustration of species.

Crioceras(coiled-horn),Lign.160,fig.2.—This shell differs from the Ammonites in the turns of the spire beingdistant from each other. The siphuncle is continuous, and the septa are regularly divided into six lobes. I have found specimens of this genus in the Chalk-marl at Hamsey, and in the White Chalk, near Lewes (Foss. South D.tab. xxiii.fig.9).

Lign. 160. Shells of the family Ammonitidæ.Chalk and Greensand.Fig.1.—Toxoceras Emericianum, and its septum.Hamsey.2.—Crioceras Puzosianum.(M. D’Orbigny.)Lewes.3.—Ancyloceras furcatum, and its septum.France.

In the genusAncyloceras(incurved horn),Lign.160,fig.3, the whorls are separate, and, at first, spiral (likeCrioceras); but afterwards the shell is prolonged, and then inflected at the large extremity, like a Scaphite, but the whorls are not contiguous.

A very large species ofAncylocerasoccurs in the Kentish Rag, near Maidstone, some specimens of which are eighteen inches in length. It is figured and described, by the name ofScaphites Hillsii, in the admirable Memoir of Dr. Fitton on the Strata below the Chalk (Geol. Trans.vol. iv. pl. xv.); the present genus was not then established. The Shanklin Sand in the Isle of Wight also contains a gigantic species, which is figured and described by Mr. J. D. Sowerby, in theGeol. Trans., asScaphites gigas.Ancylocerasoccurs also in the Oolite.

TOXOCERAS. HAMITES.

InToxoceras(bow-horn),Lign.160,fig.1, the shell is slightly curved, like a horn. Two or three species ofToxocerasare found at Hamsey. The tubercles, in the casts, are the bases of spines, with which the back of the shell was armed, as I have ascertained by examples examined in the rock (seeFoss. South D.tab. xxiii.fig.1). The specimens figured of the above two genera occur in theNeocomianstrata of France.

Hamites(hook-shaped).Lign.161,fig.1.—Shell involute, spiral, the turns not contiguous; spire irregular, elliptical; the large end reflected towards the spire. The termHamite, proposed by the late Mr. Parkinson, was formerly given to all the fragments of sub-cylindrical chambered shells, that were bent, or slightly hooked; and the generaAncyloceras,Toxoceras, &c., have been separated from them, by M. D’Orbigny. But from fossils recently obtained from Cretaceous strata in Pondicherry, and other parts of India, it seems probable that these genera will be found to merge into each other; at present it is convenient to keep up the distinction. The Hamites are distinguished from Ancyloceras, which they most resemble, by their elliptical, irregular spire.

Ptychoceras(folded horn).Lign.161,fig.4.—This is another genus formed from the Hamites. The shell is bentdouble in the shape of a siphon, and the limbs are united together. The specimen figured is from theNeocomianstrata of the Lower Alps.

Lign. 161. Hamites, etc. from the Chalk-marl.Fig.1.—Hamites cylindraceus, with part of the shell. (M. D’Orbigny.)3.—Baculites baculoides, with the mouth entire.Hamsey.3.—Part of the stem of the same species, showing the sinuous septa. A detached septum is figured above.4.—Ptychoceras Emericianum.(M. D’Orbigny.)

BACULITES.

Baculites(staff-like).Lign.161,figs.2 and 3.—This, as the name implies, is a straight, elongated, conical, chambered shell; the upper part is destitute of septa, and probably contained the body of the animal.

In my early researches in the Chalk-marl of Hamsey, I discovered numerous solid, oval, and cylindrical pipes of marl, with scarcely any vestige of organic structure, whose origin it was impossible to determine. At length I found the specimen,Lign.161,fig.2, which showed the perfect aperture of a chambered shell; and afterwards I found portions which displayed the foliated septa. (Foss. South D.tab. xxiii.figs.5, 6, 7.) The Baculite, when perfect, is elongated to a point; the septa are very numerous and foliated; the siphuncle is situated on the margin. I have a splendid specimen from the Chalk of France, (collected byM. Alex. Brongniart,) which is composed of distinct casts of the cells, held together by the deep inflections of their margins, in the same manner as are the sparry casts of Ammonites, previously described.[421]

[421]SeeBd.pl. xliv,fig.5.

The Galt, near Folkstone, abounds in fossils of the above genera, principally ofHamites; and the nacreous substance of the shells is very often preserved. From the Chalk-marl near Dover, Southbourn, Ringmer, and Southerham, near Lewes, and from Clayton, near Hurstpierpoint, in Sussex, I have obtained examples of several species.

SCAPHITES.

Scaphites(boat-like).Lign.162.—This name was given by Mr. Parkinson (Org. Rem.vol. iii. pl. x. SeePict. Atlas) to some small chambered shells from the Chalk and Shanklin Sand, of a boat-like form, with the inner whorls coiled up in a spire, and half hidden by the outer chamber, which becomes contracted and recurved on itself, is destitute of septa, and terminates in an oval or transverse mouth. The siphuncle is dorsal. AnAncylocerasclosely coiled would be a Scaphite. Hamsey marl-pit yielded to my early researches the first Scaphites discovered in the British strata, together with Turrilites, and other cephalopodous shells, previously unknown in England.[422]The Scaphite is of an ellipticalform, the spire and the mouth approaching close to each other; the spire occupies about one-half of the shell. Except the thick outer lip or margin of the aperture, which is almost constantly found changed into pyrites, it is rarely that any vestige of the shell remains. The same mineral constitutes casts of the spiral part; and these, when separated from the other portion, might be taken for Ammonites; seefig.2. There are two varieties at Hamsey; one, with the surface covered by fine transverse striæ, which arise singly from the inner margins, and bifurcate on the dorsal part;fig.1. The other is also striated, but has a row ofprominent ribs on the inner half of the broad central portion of the shell;fig.4. Scaphites occur in the Upper Green Sand of Dorsetshire, and in the Chalk-marl in several places in England; and at Rouen, in France; and a large species,S. Cuvieri, has been found in New Jersey.

[422]Sow. Min. Conch, vol, i. p. 53.

Lign. 162. Scaphites.Chalk-marl.Hamsey.

Lign. 163. Turrilites.Chalk-marl.

TURRILITES.

Turrilites.Lign.163.—Shell spiral, more or less conical, coiled obliquely round an axis, and turriculated. Spire sinistral, whorls contiguous, apparent, with a perforated umbilicus. Edges of septa very sinuous. Siphuncle continuous,situated either on the external convexity, or near the suture at the base of the wreath.

The discovery of three species of these elegant shells rewarded my researches in the little marl-pit at Hamsey, already noticed, and were the first examples of the genus found in England.[423]Like the Ammonites, Scaphites, Hamites, &c. with which they are associated, theTurrilitesof our Chalk-marl seldom possess any traces of their shells. The specimens are solid and tolerably sharp casts, with occasional indications of the septa, and more rarely of the siphunculus. They vary in size from two or three inches to two feet in length; and are frequently more or less elliptical, from compression. The three species which generally occur in the Sussex and Kentish chalk, areT. costatus,Lign.163,fig.2;T. tuberculatus(Foss. South D.pl. xxiv.fig.7), characterised by its four rows of tubercles; andT. undulatus(Foss. South D.pl. xxiv.fig.8), the wreaths of which are ornamented with plain, slightly undulated, transverse ribs. These are all reversed, orsinistralshells; that is, the spire is twisted to the left, the aperture being on the right hand of the observer when the shell is placed on its apex, as infig.1. Several other species of Turrilites occur in the Chalk of France,[424]one of which,T. catenatus, is representedLign.163,fig.1.

[423]Sow. Min. Conch, tab. xxxvi.[424]See M. D’Orbigny’s Paléontologie Française.

[423]Sow. Min. Conch, tab. xxxvi.

[424]See M. D’Orbigny’s Paléontologie Française.

Some of the Turrilites attain a considerable magnitude. The largest found in England is a specimen ofT. tuberculatus(Min. Conch.tab. lxxiv.), from Middleham, in the parish of Ringmer, near Lewes; when perfect, it must have been full two feet in length: it consists of six wreaths, the siphuncle, in the state of pyrites, appearing in three or four; portions of the nacreous internal layer of the shell remain.[425]In some specimens in my possession, the form of the aperture, andthe termination of the columella, are distinctly shown; as in the fine example the last whorl of which is represented inLign.164.

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