Ammonite

“ We have already spoken of the Ammonite, but we give here a specimen of a rare kind, preserved in the fine clay near Chippenham. The form of this ammonite is more remarkable 166than that of any other; its delicate nautilus shell has been sadly compressed, and some of its external protuberances have been broken off, and are here restored by dotted lines; but, more striking still, the delicate horn-like structure that terminated its mouth or aperture has been perfectly embalmed by Nature’s kindly hand.
AM. JASON, OR AM. ELIZABETHÆ. Oolite. ”

“ These complicated edges of the septa form 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. ”

“ 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.
Plate III.
Polished section of an Ammonite. ”

“ The geographical distribution of Ammonites in the ancient world, seems to have partaken of that universality, we find so common in the animals and vegetables of a former condition of our globe, and which differs so remarkably from the varied distribution that prevails among existing forms of organic life. We find, the same genera, and, in a few cases, the same species of Ammonites, in strata, apparently of the same age, not only throughout Europe, but also in distant regions of Asia, and of North and South America. ”

“ We have noticed that in the Devonian the sutures of some of the chambered shells become angled, evolving the Goniatite type. The sutures now become lobed and corrugated in Ceratites. The process was carried still farther, and the sutures were elaborately frilled in the great order of the Ammonites. It was in the Jurassic that the Ammonites reached their height. No fossils are more abundant or characteristic of their age. Great banks of their shells formed beds of limestone in warm seas the world over.
The ammonite stem branched into a most luxuriant variety of forms. ”

“ In the shale we find numerous minute Ammonites, sorely weathered; in the sandstone, Belemnites, some of them of great size; and dark carbonaceous markings, passing not unfrequently into a glossy cubical coal. At the foot of the cliff I picked up an ammonite of considerable size and well-marked character,—the Ammonites Murchisonæ, first discovered on this coast by Sir R. Murchison about fifteen years ago. It measures, when full grown, from six to seven inches in diameter; the inner whorls, which are broadly visible, are ribbed ”

“ The foliated edges of these transverse plates have regulated the foliations of the calcareous casts, which, after the shell has perished, remain locked into one another, like the sutures of a skull. The substance of the casts in all these cases is pure crystalline carbonate of lime, introduced by infiltration through the pores of the decaying shell. Each species of Ammonite has its peculiar form of air-chamber, depending on the specific form of its transverse plates. Analogous variations in the form of the air-chambers are co-extensive with the entire range of species in the family of Nautili. ”

“ By removing them in succession in the adult form we find an illustration of the evolution of the elaborate shell of the Jurassic Ammonite. It is an admirable testimony to the validity of the embryonic law we have often quoted—that the young animal is apt to reproduce the past stages of its ancestry—that the order of the building of the shell in the late Ammonite corresponds to the order we trace in its development in the geological chronicle. About a thousand species of Ammonites were developed in the Mesozoic, and none survived the Mesozoic. ”

“ When we recollect that throughout both these great formations, the still more numerous extinct family of Ammonites is co-extensive with the Belemnites; and that each species of Ammonite exhibits also contrivances, more complex and perfect than those retained in the few existing cognate genera of Cephalopods; we cannot but infer that these extinct families filled a larger space, and performed more important functions among the inhabitants of the ancient seas, than are assigned to their few living representatives in our modern oceans. ”

“ It is a curious fact, that contrivances, similar to those which existed in some of the most early forms of Ammonite, should have been again adopted in some of the most recent species of fossil Nautili, in order to afford similar compensation for weakness that would otherwise have been produced by aberrations from the normal structure of the genus Nautilus. ”

“ British or pre-Saxon] Dorsetshire barrow opened in the eighteenth century by Colonel Drax. Douglas, who saw the specimens, figures one of them in his Nenia Britannica [763] . Canon Greenwell found a portion of an ammonite lying beside a skeleton in one of the Yorkshire mounds [764] . It is well to remember that a black ammonite, of which the species is not stated, is associated with the religious ceremonies of the Brahmans, being regarded by the devout as the embodiment of Vishnu [765] . Some of the larger fish teeth, occurring as fossils, also come in our list. ”

“ More than in many other mollusks the organization of the ammonite is reflected in the characters of the shell and the infancy, maturity and decline of the group to which it belongs is, to the qualified student, pictured in the characteristics of the successive portions of the lustrous coil of the fossil shell. ”

“ Moreover, the margin of the mature Ammonite is in some species reflected in a kind of scroll, like the thickened margin of the shell of the garden snail, giving to this part a strength which would apparently be needless to an internal shell. (See Pl. 37. Fig. 3. d.) The presence of spines also in certain species, (as in A. Armatus, A. Sowerbii,) affords a strong argument against the theory of their having been internal shells. ”

“ In this there are no corals, but great abundance of cephalopoda of the genera Ammonite and Belemnite. (See fig. 277.) In some of the clay of very fine texture ammonites are very perfect, although somewhat compressed, and are seen to be furnished on each side of the aperture with a single horn-like projection (see fig. 278.) . These were discovered in the cuttings of the Great Western Railway, near Chippenham, in 1841, and have been described by Mr. Pratt. [262-A]
Fig. ”

“ In more than two hundred known species of Ammonites, the transverse plates present some beautifully varied modifications of this foliated expansion at their edges; the effect of which, in every case, is to increase the strength of the outer shell, by multiplying the subjacent points of resistance to external pressure. We know that the pressure of the sea, at no great depth, will force a cork into a bottle filled with air, or crush a hollow cylinder or sphere of thin copper ”

“ Wherever access to it can be had, we find it richly fossiliferous; but its organisms, with the exception of its Belemnites, are very imperfectly preserved. I dug up from under the trap-blocks some of the common Liasic Ammonites of the north-eastern coast of Scotland, a few of the septa of a large Nautilus, broken pieces of wood, and half-effaced casts of what seems a branched coral; but only minute portions of the shells have been converted into stone; here and there a few chambers in the whorls of an Ammonite or Nautilus, though the outline of the entire organism lies impressed in the shale ”

“ Within these limits, each formation is characterised by particular species, the number of individuals being often very great, and the size which is sometimes attained being nothing short of gigantic. In the Lias, particular species of Ammonites may succeed one another regularly, each having a more or less definite horizon, which it does not transgress. It is thus possible to distinguish a certain number of zones, each characterised by a particular Ammonite, together with other associated fossils. ”

“ Ammon′iaphone, an instrument invented about 1880, said to improve the quality of the singing and speaking voice, being an apparatus for inhaling peroxide of hydrogen and free ammonia.—adj. Ammōn′iated, containing ammonia.—n. Ammon′ium, the hypothetical base of ammonia. [From sal-ammoniac, or smelling-salts, first obtained by heating camel's dung in Libya, near the temple of Jupiter Ammon.]
Ammonite, am′mon-īt, n. the fossil shell of an extinct genus of molluscs, so called because they resemble the horns on the statue of Jupiter Ammon, worshipped as a ram. ”

“ I have many specimens from the lias of Whitby, of the Ammonites Communis, in which the outer chamber thus filled with spar, occupies nearly the entire last whorl of the shell, its largest extremity only being filled with lias. From specimens of this kind we also learn, that the animal inhabiting the shell of an Ammonite, had no ink-bag; if such an organ existed, traces of its colour must have been found within the cavity which contained the body of the animal at the moment of its death. The protection of a shell seems to have rendered the presence of an ink-bag superfluous. ”

“ On examining the proofs of Contrivance and Design that pervade the testaceous remains of the family of Ammonites, we find, in every species, abundant evidence of minute and peculiar mechanisms, adapting the shell to the double purpose of acting as a float, and of forming a protection to the body of its inhabitant. ”

“ Con. ↑ The external chamber (a) is larger than the rest, and swelling; and capable of containing a considerable portion of the animal. The outer shell was thin, and strengthened, like the Ammonite, by oblique ribs. Near the posterior margin of the shell, the transverse plates are pierced by a Siphuncle (Pl. 44, 5b, c,) . This position of the Siphuncle, and the sinuous form and denticulated edges of the transverse plates, are characters which the Baculite possesses in common with the Ammonite. ↑ Both these forms of Hamite bear the same relation to Ammonites that Lituites bear to Nautili ”

“ Back view of Ammonites sphæricus, from the limestone of Derbyshire, showing the position of the siphuncle upon the dorsal margin, with its collar advancing outwards between the two simple dorsal lobes; the lateral lobes are also simple and without foliations, and pointed inwards. ”

“ The quarries, which are in the immediate vicinity of the town, abound in Ammonites, Trigoniæ, and other shells: and some layers are entirely composed of the casts of several species. The Ammonites are principally of two kinds, viz. A. biplex and A. triplicatus, and vary in size from a few inches to upwards of three feet in diameter; the specimens are casts only, no vestiges of the shells remaining. At Aylesbury the same species occur in clay, with the shells entire (see p. 481) . A large collection may be made in a few hours ”

“ These are remarkable for the ornate markings on the surfaces of their shells, and for the beautifully waved edges of the partitions (Fig. 72a) , which, by giving a much more complete support to the sides of the shell, must have contributed greatly to the union of lightness and strength so important to the utility of the shell as a float. This type admits of all the same variety of straight, bent, and curled forms with the simpler Nautiloid type, and some of the species are of great size, Ammonites being known three feet or more in diameter. ”

“ We saw here no remains of ammonites. Numerous other species appear to be similar to those found in the limestone of the Catskill and Hellebergh mountains.
The soil, which overlays the limestone of Cincinnati, is a deep argillaceous loam, intermixed with much animal [pg067] and vegetable matter. Vegetation is here luxuriant; and many plants unknown eastward of the Alleghany mountains, were constantly presenting themselves to our notice. Two species of æsculus are common. ”

“ The chambers are filled with semi-transparent spar. The siphunculus is seen running along the dorsal, or outer margins of the volutions. The dark appearances observable in several parts of the siphuncle result from the carbonization of the animal membrane with which the tube was lined in the living state.
Fig. 6. "An Oval Ammonite."—Mr. Parkinson. This is evidently the cast of a discoidal shell pressed into an elliptical form. In the Chalk-marl, casts of Ammonites, Nautilites, &c. are very commonly more or less distorted by compression. ”

“ AMIMONUS. Montf. Conilites ungulatus, Knorr. A species distinguished only by being slightly curved; Fam. Orthocerata, Lam.
AMMONACEA. Bl. The fourth family of the order Polythalamia, Bl. or chambered shells, described as thin, chambered, discoidal, convolute, symmetrical, generally compressed, with visible whorls. This last character is used in De Blainville's System to distinguish the Ammonacea from the Nautilacea. This family contains the genera Discorbites, Scaphites, Ammonites, and Simplegas.
AMMONACEA. Lam. The seventh family of Polythalamous Cephalopoda, Lam. ”