At Bracklesham Bay, near Chichester, in Sussex, the characteristic shells of this member of the Eocene series are best seen; among others, the huge Cerithium giganteum, so conspicuous in the calcaire grossier of Paris, where it is sometimes 2 feet in length. The volutes and cowries of this formation, as well as the lunulites and other corals, seem to favour the idea of a warm climate having prevailed, which is borne out by the discovery of a serpent Palæophis typhæus, exceeding, according to Mr. Owen, 20 feet in length, and allied to the Boa, Python, Coluber, and Hydrus. The compressed form and diminutive size of certain caudal vertebræ indicate so much analogy with Hydrus as to induce the Hunterian professor to pronounce the extinct ophidian to have been marine.[199-B] He had previously combated with so much success the evidence advanced, to prove the existence in the Northern Ocean of sea-serpents in our own times, that he will not be suspected of any undue bias in contending for their former existence in the British Eocene seas. The climate, however, of the Middle Eocene period was evidently far more genial; and amongst the companions of the sea-serpent of Bracklesham was an extinct Gavial (Gavialis Dixoni, Owen), and numerous fish, such as now frequent the seas of warm latitudes, as the sword-fish (see fig. 172. p. 200.) and gigantic rays of the genus Miliobates. (See fig. 173.)

Out of 193 species of testacea procured from the Bagshot and Bracklesham beds in England, 126 occur in the French calcaire grossier. It was clearly, therefore, coeval with that part of the Parisian series more nearly than with any other. The Nummulites lævigatus (see fig. 174.), a fossil characteristic of the lower beds of the calcaire grossier, is abundant at Bracklesham.

London clay proper (3. a, Table, p. 197.).—This formation underlies the preceding, and consists of tenacious brown and blueish grey clay, with layers of concretions called septaria, which abound chiefly in the brown clay, and are obtained in sufficient numbers from the cliffs near Harwich, and from shoals of the Essex coast, to be used for making Roman cement. The principal localities of fossils in the London clay are Highgate Hill, near London, the island of Sheppey, and Bognor in Hampshire. Out of 133 fossil shells, Mr. Prestwich found only 20 to be common to the calcaire grossier (from which 600 species have been obtained), while 33 are common to the lits coquilliers (p. 196.), in which only 200 species are known in France. We may presume, therefore, that the London clay proper is older than the calcaire grossier. This may perhaps remove a difficulty which M. Adolphe Brongniart has experienced when comparing the Eocene Flora of the neighbourhoods of London and Paris. The fossil species of the island of Sheppey, he observes, indicate a much more tropical climate than the Eocene Flora of France, which has been derived principally from the "gypseous series." The latter resembles the vegetation of the borders of the Mediterranean rather than that of an equatorial region.

Mr. Bowerbank, in a valuable publication on the fossil fruits and seeds of the island of Sheppey, near London, has described no less than thirteen fruits of palms of the recent type Nipa, now only found in the Molucca and Philippine islands. (See fig. 175.) These plants are allied to the cocoa-nut tribe on the one side, and on the other to the Pandanus, or screw-pine. Species of cocoa-nuts are also met with, and other kinds of palms; also three species of Anona, or custard-apple; cucurbitaceous fruits, also (the gourd and melon family), are in considerable abundance. Fruits of various species of Acacia are in profusion; and, although less decidedly tropical, imply a warm climate.

The marine shells of the London clay confirm the inference derivable from the plants and reptiles of a high temperature. Thus, many species of Conus, Mitra, and Voluta occur, a large Cypræa, a very large Rostellaria, and shells of the genera Terebellum, Cancellaria, Crassatella, and others, with four or more species of Nautilus (see fig. 182.) and other cephalopoda of extinct genera, one of the most remarkable of which is the Belosepia.[202-A] (See fig. 183.)

Strata of Kyson in Suffolk.—At Kyson, a few miles east of Woodbridge, a bed of Eocene clay, 12 feet thick, underlies the red crag. Beneath it is a deposit of yellow and white sand, of considerable interest, in consequence of many peculiar fossils contained in it. Its geological position is probably the lowest part of the London clay proper. In this sand has been found the first example of a fossil quadrumanous animal discovered in Great Britain, namely, the teeth and part of a jaw, shown by Mr. Owen to belong to a monkey of the genus Macacus (see fig. 184.). The mammiferous fossils, first met with in the same bed, were those of an opossum (Didelphys) (see fig. 185.), and an insectivorous bat (fig. 186.), together with many teeth of fishes of the shark family. Mr. Colchester in 1840 obtained other mammalian relics from Kyson, among which Mr. Owen has recognized several teeth of the genus Hyracotherium, and the vertebræ of a large serpent, probably a Palæophis. As the remains both of the Hyracotherium and Palæophis were afterwards met with in the London clay, as before remarked, these fossils confirmed the opinion previously entertained, that the Kyson sand belongs to the Eocene period. The Macacus, therefore, constitutes the first example of any quadrumanous animal found in strata as old as the Eocene, or so far from the equator as lat. 52° N. It was not until after the year 1836 that the existence of any fossil quadrumana was brought to light. Since that period they have been found in France, India, and Brazil.

Mottled or Plastic Clays, &c. (3. b, Table, p. 197.).—No formations can be more dissimilar on the whole in mineral character than the Eocene deposits of England and Paris; those of our own island being almost exclusively of mechanical origin,—accumulations of mud, sand, and pebbles; while in the neighbourhood of Paris we find a great succession of strata composed of a coarse white limestone, and compact siliceous limestone with beds of crystalline gypsum and siliceous sandstone, and sometimes pure flint used for millstones. Hence it is by no means an easy task to institute an exact comparison between the various members of the English and French series, and to settle their respective ages. It is clear that a continual change was going on in the fauna and flora by the coming in of new species and the dying out of others; and contemporaneous changes of geographical conditions were also in progress in consequence of the rising and sinking of the land and bottom of the sea. A particular subdivision, therefore, of time was occasionally represented in one area by land, in another by an estuary, in a third by the sea, and even where the conditions were in both areas of a marine character, there was often shallow water in one, and deep sea in another, producing a want of agreement in the state of animal life.

At the commencement, however, of the Eocene formations in France and England, we find an exception to this rule, for a marked similarity of mineral character reigns in the lowest division, whether in the basins of Paris, Hampshire, or London. This uniformity of aspect must be seen in order to be fully appreciated, since the beds consist simply of sand, mottled clays, and well-rolled flint pebbles, derived from the chalk, and varying in size from that of a pea to an egg. These strata may be seen at Reading, at Blackheath, near London, and at Woolwich. In some of the lowest of them, banks of oysters are observed, consisting of Ostrea bellovicina, so common in France in the same relative position, and Ostrea edulina, scarcely distinguishable from the living eatable species. In this formation at Bromley, Dr. Buckland found one large pebble to which five full-grown oysters were affixed, in such a manner as to show that they had commenced their first growth upon it, and remained attached to it through life.

In several places, as at Woolwich on the Thames, at Newhaven in Sussex, and elsewhere, a mixture of marine and freshwater testacea distinguishes this member of the series. Among the latter, Melania inquinata (see fig. 188.) and Cyrena cuneiformis are very common. They probably indicate points where rivers entered the Eocene sea.

Before the minds of geologists had become familiar with the theory of the gradual sinking of the land, and its conversion into sea at different periods, and the consequent change from shallow to deep water, the freshwater and littoral character of this inferior group appeared strange and anomalous. After passing through many hundred feet of London clay, proved by its fossils to have been deposited in salt water of considerable depth, we arrive at beds of fluviatile origin. Thick masses, also, of shingle indicate the proximity of land, where the flints of the chalk were rolled into sand and pebbles, and spread continuously over wide spaces, as in the Isle of Wight, in the south of Hampshire, and near London, always appearing at the bottom of the Eocene series. It may be asked why they did not constitute simply a narrow littoral zone, such as we might look for in strata formed at a moderate distance from the shore. In answer to this inquiry, the student must be reminded, that wherever a gently-sloping land is gradually sinking and becoming submerged, shingle may be heaped up successively over a wide area, although marine currents have no power of dispersing it simultaneously over a large space. In such cases it is not the shingle which recedes from the coast, but the coast which recedes from the shingle, which is formed one mass after another as often as successive portions of the land are converted into sea and others into a sea beach.

The London area appears to have been upraised before that of Hampshire, so that it never became the receptacle of the Barton clays, nor of the overlying fluvio-marine and freshwater beds of Hordwell and the north part of the Isle of Wight. On the other hand, the Hampshire Eocene area seems to have emerged before that of Paris, so that no marine beds of the Upper Eocene era were ever thrown down in Hampshire.

Nummulitic formation of the Alps and Pyrenees.—It has long been matter of controversy, whether the nummulitic rocks of the Alps and Pyrenees should be regarded as Eocene or Cretaceous; but the number of geologists of high authority who regard this important group as belonging to the lowest tertiary system of Europe has for many years been steadily increasing. The late M. Alex. Brongniart first declared the specific identity of many of the shells of this formation with those of the marine strata near Paris, although he obtained them from the summit of the Diablerets, one of the loftiest of the Swiss Alps, which rises more than 10,000 feet above the level of the sea.

Deposits of the same age, found on the flanks of the Pyrenees, contain also a great number of shells common to the Paris and London areas, and three or four species only which are common to the cretaceous formation.

The calcareous division consists often of a compact crystalline marble, full of nummulites (see fig. 189.), shells of the class Foraminifera.

The nummulitic limestone of the Alps is often of great thickness, and is immediately covered by another series of strata of dark-coloured slates, marls, and fucoidal sandstones, to the whole of which the provincial name of "flysch" has been given in parts of Switzerland. The researches of Sir Roderick Murchison in the Alps in 1847 enable us to refer the whole of these beds to the Eocene period, and it seems probable that they most nearly coincide in age with the Lower Eocene. They enter into the disturbed and loftiest portions of the Alpine chain, to the elevation of which they enable us therefore to assign a comparatively modern date.

The nummulitic formation, with its characteristic fossils, plays a far more conspicuous part than any other tertiary group in the solid framework of the earth's crust, whether in Europe, Asia, or Africa. It often attains a thickness of many thousand feet, and extends from the Alps to the Apennines. It is found in the Carpathians, and in full force in the north of Africa, as, for example, in Algeria and Morocco. It has also been traced from Egypt into Asia Minor, and across Persia by Bagdad to the mouths of the Indus. It occurs not only in Cutch, but in the mountain ranges which separate Scinde from Persia, and which form the passes leading to Caboul; and it has been followed still farther eastward into India.

Some members of this lower tertiary formation in the central Alps, including even the superior strata called flysch, have been converted into crystalline rocks, and changed into saccharoid marble, quartz, rock, and mica-schist.[206-A]

EOCENE STRATA IN THE UNITED STATES.

In North America the Eocene formations occupy a large area bordering the Atlantic, which increases in breadth and importance as it is traced southwards from Delaware and Maryland to Georgia and Alabama. They also occur in Louisiana and other states both east and west of the valley of the Mississippi. At Claiborne in Alabama no less than four hundred species of marine shells, with many echinoderms and teeth of fish, characterize one member of this system. Among the shells the Cardita planicosta, before mentioned (fig. 171. p. 199.), is in abundance; and this fossil, and some others identical with European species, or very nearly allied to them, make it highly probable that the Claiborne beds agree in age with the central or Bracklesham group of England, and the calcaire grossier of Paris.[206-B]

Higher in the series is a remarkable calcareous rock, formerly called "the nummulite limestone," from the great number of discoid bodies resembling nummulites which it contains, fossils now referred by A. d'Orbigny to the genus Orbitoides, which has been demonstrated by Dr. Carpenter to belong to the Foraminifera.[206-C] The following section will enable the reader to understand the position of the three subdivisions of the series, Nos. 1, 2, and 3., the relations of which I ascertained in Clarke County, between the rivers Alabama and Tombeckbee.

No. 2. (fig. 190.) is a white limestone, sometimes soft and argillaceous, but in parts very compact and calcareous. It contains several peculiar corals, and a large Nautilus allied to N. zigzag, also in its upper bed a gigantic cetacean, called Zeuglodon by Owen.[207-A]

The colossal bones of this cetacean are so plentiful in the interior of Clarke County as to be characteristic of the formation. The vertebral column of one skeleton found by Dr. Buckley at a spot visited by me, extended to the length of nearly 70 feet, and not far off part of another backbone nearly 50 feet long was dug up. I obtained evidence, during a short excursion, of so many localities of this fossil animal within a distance of 10 miles, as to lead me to conclude that they must have belonged to at least forty distinct individuals.

Mr. Owen first pointed out that the huge animal was not reptilian, since each tooth was furnished with double roots (see fig. 191.), implanted in corresponding double sockets; and his opinion of the cetacean nature of the fossil was afterwards confirmed by Dr. Wyman and Professor R. W. Gibbes. That it was an extinct species of the whale tribe has since been placed beyond all doubt by the discovery of the entire skull of another fossil of the same family, found to have the double occipital condyles only met with in mammals, and the convoluted tympanic bones which are characteristic of cetaceans.

Near the junction of No. 2. and the incumbent limestone, No. 3., next to be mentioned, are strata characterized by the following shells: Spondylus dumosus (Plagiostoma dumosum, Morton), Pecten Poulsoni, Pecten perplanus, and Ostrea cretacea.

No. 3. (fig. 190.) is a white limestone, for the most part made up of the Orbitoides of d'Orbigny before mentioned (p. 206.), formerly supposed to be a nummulite, and called N. Mantelli, mixed with a few lunulites and small corals and shells.[208-A] The origin of this cream-coloured soft stone, like that of our white chalk, which it much resembles, is, I believe, due to the decomposition of the orbitoides. The surface of the country where it prevails is sometimes marked by the absence of wood, like our chalk downs, or is covered exclusively by the Juniperus Virginiana, as certain chalk districts in England by yew trees and juniper.

Some of the shells of this limestone are common to the Claiborne beds, but many of them are peculiar.

It will be seen in the section (fig. 190. p. 155.) that the strata, Nos. 1, 2, 3., are, for the most part, overlaid by a dense formation of sand or clay without fossils. In some points of the bluff or cliff of the Alabama river, at Claiborne, the beds Nos. 1, 2., are exposed nearly from top to bottom, whereas at other points the newer formation, No. 4., occupies the face of nearly the whole cliff. The age of this overlying mass has not yet been determined, as it has hitherto proved destitute of organic remains.

The burr-stone strata of the Southern States contain so many fossils agreeing with those of Claiborne, that it doubtless belongs to the same part of the Eocene group, though I was not fortunate enough to see the relations of the two deposits in a continuous section. Mr. Tuomey considers it as the lower portion of the series. It may, perhaps, be a form of the Claiborne beds in places where lime was wanting, and where silex, derived from the decomposition of felspar, predominated. It consists chiefly of slaty clays, quartzose sands, and loam, of a brick red colour, with layers of chert or burr-stone, used in some places for millstones.

CHAPTER XVII.

CRETACEOUS GROUP.

Having treated in the preceding chapters of the tertiary strata, we have next to speak of the uppermost of the secondary groups, called the Chalk or Cretaceous (No. 6. Table, p. 103.), because in those parts of Europe where it was first studied its upper members are formed of that remarkable white earthy limestone, termed chalk (creta). The inferior division consists, for the most part, of clays and sands, called Greensand, because some of the sands derive a bright green colour from intermixed grains of chloritic matter. The cretaceous strata in the north-west of Europe may be thus divided[209-A]:

Maestricht Beds.—On the banks of the Meuse, at Maestricht, reposing on ordinary white chalk with flints, we find an upper calcareous formation about 100 feet thick, the fossils of which are, on the whole, very peculiar, and all distinct from tertiary species. Some few are of species common to the inferior white chalk, among which may be mentioned Belemnites mucronatus (see fig. 197.) and Pecten quadricostatus. Besides the Belemnite there are other genera, such as Ammonite, Baculite, and Hamite, never found in strata newer than the cretaceous, but frequently met with in these Maestricht beds. On the other hand, Volutes and other genera of univalve shells, usually met with only in tertiary strata, occur.

The upper part of the rock, about 20 feet thick, as seen in St. Peter's Mount, in the suburbs of Maestricht, abounds in corals, often detachable from the matrix; and these beds are succeeded by a soft yellowish limestone 50 feet thick, extensively quarried from time immemorial for building. The stone below is whiter, and contains occasional nodules of grey chert or chalcedony.

M. Bosquet, with whom I lately examined this formation (August, 1850), pointed out to me a layer of chalk from 2 to 4 inches thick, containing green earth and numerous encrinital stems, which forms the line of demarcation between the strata containing the fossils peculiar to Maestricht and the white chalk below. The latter is distinguished by regular layers of black flint in nodules, and by several shells, such as Terebratula carnea (see fig. 201.), wholly wanting in beds higher than the green band. Some of the organic remains, however, for which St. Peter's Mount is celebrated, occur both above and below that parting layer, and, among others, the great marine reptile, called Mosasaurus, a saurian supposed to have been 24 feet in length, of which the entire skull and a great part of the skeleton have been found. Such remains are chiefly met with in the soft freestone, the principal member of the Maestricht beds.

Chalk of Faxoe.—In the island of Seeland, in Denmark, the newest member of the chalk series, seen in the sea-cliffs at Stevens Klint resting on white chalk with flints, is a yellow limestone, a portion of which, at Faxoe, where it is used as a building-stone, is composed of corals, even more conspicuously than is usually observed in recent coral reefs. It has been quarried to the depth of more than 40 feet, but its thickness is unknown. The imbedded shells are chiefly casts, many of them of univalve mollusca, which, as they strictly belong to the Cretaceous era, are worthy of notice, since such forms, whether spiral or patelliform, are wanting in the white chalk of Europe generally. Thus, there are two species of Cypræa, one of Oliva, two of Mitra, four of the genus Cerithium, six of Fusus, two of Trochus, one Patella, one Emarginula, &c., on the whole, more than thirty univalves, spiral or patelliform, not one of which is common to the white chalk. At the same time, a large proportion of the accompanying bivalve shells, echinoderms, and zoophytes, are specifically identical with fossils of older parts of the Cretaceous series. Among the cephalopoda of Faxoe, may be mentioned Baculites Faujasii and Belemnites mucronatus, shells of the white chalk.

The claws and entire shell of a small crab, Brachyurus rugosus (Schlotheim), are scattered through the Faxoe stone, reminding us of similar crustaceans enclosed in the rocks of many modern coral reefs.[211-A] Some small portions of this coralline formation consist of white earthy chalk; it is, therefore, clear that this substance must have been produced simultaneously, a fact of some importance, as bearing on the theory of the origin of white chalk; for the decomposition of such corals as we see at Faxoe is capable, we know, of forming white mud, undistinguishable from chalk, and which we may suppose to have been dispersed far and wide through the ocean, in which such reefs as that of Faxoe grew.

White Chalk (2. and 3. Tab. p. 209.).—The highest beds of chalk in England and France consist of a pure, white, calcareous mass, usually too soft for a building stone, but sometimes passing into a more solid state. It consists, almost purely, of carbonate of lime; the stratification is often obscure, except where rendered distinct by interstratified layers of flint, a few inches thick, occasionally in continuous beds, but oftener in nodules, and recurring at intervals from 2 to 4 feet distant from each other.

This upper chalk is usually succeeded, in the descending order, by a great mass of white chalk without flints, below which comes the chalk marl, in which there is a slight admixture of argillaceous matter. The united thickness of the three divisions in the south of England equals, in some places, 1000 feet.[211-B]

The annexed section, fig. 193., will show the manner in which the white chalk extends from England into France, covered by the tertiary strata described in former chapters, and reposing on lower cretaceous beds.

Among the conspicuous forms of mollusca wholly foreign to the tertiary and recent periods, and which we meet with in the white chalk, are the Belemnite, Ammonite, Baculite, and Turrilite, all genera of Cephalopoda, a family to which the living cuttle-fish and nautilus belong.

Among the brachiopoda in the white chalk, the Terebratulæ are very abundant. These shells are known to live at the bottom of the sea, where the water is tranquil and of some depth (see figs. 198, 199, 200, 201.). With these are associated some forms of oyster (see figs. 202. and 204.), and other bivalves (figs. 203, 205, 206, 207, 208.).