CHAPTER XVI.

EOCENE FORMATIONS—continued.

Subdivisions of the Eocene group in the Paris basin — Gypseous series — Extinct quadrupeds — Impulse given to geology by Cuvier's osteological discoveries — Shelly sands called sables moyens — Calcaire grossier — Miliolites — Calcaire siliceux — Lower Eocene in France — Lits coquilliers — Sands and plastic clay — English Eocene strata — Freshwater and fluvio-marine beds — Barton beds — Bagshot and Bracklesham division — Large ophidians and saurians — Lower Eocene and London Clay proper — Fossil plants and shells — Strata of Kyson in Suffolk — Fossil monkey and opossum — Mottled clays and sands below London Clay — Nummulitic formation of Alps and Pyrenees — Its wide geographical extent — Eocene strata in the United States — Section at Claiborne, Alabama — Colossal cetacean — Orbitoid limestone — Burr stone.

From what was said in the two preceding chapters, it has already appeared that we have in England no true chronological representative of the Miocene faluns of the Loire, and none of the Upper Eocene group described in the last chapter. But, when we descend to the middle and inferior divisions of the Eocene system of France, we find that they have their equivalents in Great Britain.

MIDDLE EOCENE.—FRANCE.

Gypseous series (2. a, Table, [p. 175.]).—Next below the upper marine sands of the neighbourhood of Paris, we find a series of white and green marls, with subordinate beds of gypsum. These are most largely developed in the central parts of the Paris basin, and, among other places, in the Hill of Montmartre, where its fossils were first studied by M. Cuvier.

The gypsum quarried there for the manufacture of plaster of Paris occurs as a granular crystalline rock, and, together with the associated marls, contains land and fluviatile shells, together with the bones and skeletons of birds and quadrupeds. Several land plants are also met with, among which are fine specimens of the fan palm or palmetto tribe (Flabellaria). The remains also of freshwater fish and of crocodiles and other reptiles, occur in the gypsum. The skeletons of mammalia are usually isolated, often entire, the most delicate extremities being preserved; as if the carcasses, clothed with their flesh and skin, had been floated down soon after death, and while they were still swoln by the gases generated by their first decomposition. The few accompanying shells are of those light kinds which frequently float on the surface of rivers, together with wood.

M. Prevost has therefore suggested that a river may have swept away the bodies of animals, and the plants which lived on its borders, or in the lakes which it traversed, and may have carried them down into the centre of the gulf into which flowed the waters impregnated with sulphate of lime. We know that the Fiume Salso in Sicily enters the sea so charged with various salts that the thirsty cattle refuse to drink of it. A stream of sulphureous water, as white as milk, descends into the sea from the volcanic mountain of Idienne on the east of Java; and a great body of hot water, charged with sulphuric acid, rushed down from the same volcano on one occasion, and inundated a large tract of country, destroying, by its noxious properties, all the vegetation.[191-A] In like manner the Pusanibio, or "Vinegar River," of Colombia, which rises at the foot of Puracé, an extinct volcano, 7,500 feet above the level of the sea, is strongly impregnated with sulphuric and muriatic acids and with oxide of iron. We may easily suppose the waters of such streams to have properties noxious to marine animals, and in this manner the entire absence of marine remains in the ossiferous gypsum may be explained.[191-B] There are no pebbles or coarse sand in the gypsum; a circumstance which agrees well with the hypothesis that these beds were precipitated from water holding sulphate of lime in solution, and floating the remains of different animals.

In this formation the relics of about fifty species of quadrupeds, including the genera Paleotherium, Anoplotherium, and others, have been found, all extinct, and nearly four-fifths of them belonging to a division of the order Pachydermata, which is now represented by only four living species; namely three tapirs and the daman of the Cape. With them a few carnivorous animals are associated, among which are a species of fox and gennet. Of the Rodentia, a dormouse and a squirrel; of the Insectivora, a bat; and of the Marsupialia (an order now confined to America, Australia, and some contiguous islands), an opossum, have been discovered.

Of birds, about ten species have been ascertained, the skeletons of some of which are entire. None of them are referable to existing species.[192-A] The same remark applies to the fish, according to MM. Cuvier, and Agassiz, as also to the reptiles. Among the last are crocodiles and tortoises of the genera Emys and Trionyx.

The tribe of land quadrupeds most abundant in this formation is such as now inhabits alluvial plains and marshes, and the banks of rivers and lakes, a class most exposed to suffer by river inundations. Whether the disproportion of carnivorous animals can be ascribed to this cause, or whether they were comparatively small in number and dimensions, as in the indigenous fauna of Australia, when first known to Europeans, is a point on which it would be rash, perhaps, to offer an opinion in the present state of our knowledge.

Fig. 162.

Paleotherium magnum.

The Paleothere, above alluded to, resembled the living tapir in the form of the head, and in having a short proboscis, but its molar teeth were more like those of the rhinoceros (see [fig. 163.]). Paleotherium magnum was of the size of a horse, 3 or 4 feet high. The annexed woodcut, [fig. 162.], is one of the restorations which Cuvier attempted of the outline of the living animal, derived from the study of the entire skeleton. When the French osteologist declared in the early part of the present century, that all the fossil quadrupeds of the gypsum of Paris were extinct, the announcement of so startling a fact, on such high authority, created a powerful sensation, and from that time a new impulse was given throughout Europe to the progress of geological investigation. Eminent naturalists, it is true, had long before maintained that the shells and zoophytes, met with in many ancient European rocks, had ceased to be inhabitants of the earth, but the majority even of the educated classes continued to believe that the species of animals and plants now contemporary with man, were the same as those which had been called into being when the planet itself was created. It was easy to throw discredit upon the new doctrine by asking whether corals, shells, and other creatures previously unknown, were not annually discovered? and whether living forms corresponding with the fossils might not yet be dredged up from seas hitherto unexamined? But from the era of the publication of Cuvier's Ossements Fossiles, and still more his popular Treatise called "A Theory of the Earth," sounder views began to prevail. It was clearly demonstrated that most of the mammalia found in the gypsum of Montmartre differed even generically from any now existing, and the extreme improbability that any of them, especially the larger ones, would ever be found surviving in continents yet unexplored, was made manifest. Moreover, the non-admixture of a single living species in the midst of so rich a fossil fauna was a striking proof that there had existed a state of the earth's surface zoologically unconnected with the present order of things.

Fig. 163.

Upper molar tooth of Paleotherium magnum from Isle of Wight. (Owen's Brit. Foss. p. 317.)

Reduced one-third.

Grès de Beauchamp (2. b, Table, [p. 175.]).—In some parts of the Paris basin, sands and marls, called the Grès de Beauchamp, or Sables Moyens, divide the gypseous beds from the underlying Calcaire grossier. These sands contain more than 300 species of marine shells, many of them peculiar, but others common to the underlying marine deposit (No. 2. c.).

Calcaire grossier (2. c, Table, [p. 175.]).—The formation called Calcaire grossier consists of a coarse limestone, often passing into sand. It contains the greater number of the fossil shells which characterize the Paris basin. No less than 400 distinct species have been procured from a single spot near Grignon, where they are embedded in a calcareous sand, chiefly formed of comminuted shells, in which, nevertheless, individuals in a perfect state of preservation, both of marine, terrestrial, and freshwater species, are mingled together. Some of the marine shells may have lived on the spot; but the Cyclostoma and Limnea must have been brought thither by rivers and currents, and the quantity of triturated shells implies considerable movement in the waters.

Nothing is more striking in this assemblage of fossil testacea than the great proportion of species referable to the genus Cerithium (see [fig. 164.]). There occur no less than 137 species of this genus in the Paris basin, and almost all of them in the calcaire grossier. Now the living Cerithia inhabit the sea near the mouths of rivers, where the waters are brackish; so that their abundance in the marine strata now under consideration is in harmony with the hypothesis, that the Paris basin formed a gulf into which several rivers flowed, the sediment of some of which gave rise to the beds of clay and lignite before mentioned; while a distinct freshwater limestone, called calcaire siliceux, which will presently be described, was precipitated from the waters of others situated farther to the south.

Fig. 164.

Cerithium cinctum.[194-A]

EOCENE FORAMINIFERA.

Fig. 165. Calcarina rarispina, Desh.

Fig. 166. Spirolina stenostoma, Desh.

Fig. 167. Triloculina inflata, Desh.

Fig. 168. Clavulina corrugata, Desh.

In some parts of the calcaire grossier round Paris, certain beds occur of a stone used in building, and called by the French geologists "Miliolite limestone." It is almost entirely made up of millions of microscopic shells, of the size of minute grains of sand, which all belong to the class Foraminifera. Figures of some of these are given in the annexed woodcut. As this miliolitic stone never occurs in the Faluns, or Miocene strata of Brittany and Touraine, it often furnishes the geologist with a useful criterion for distinguishing the detached Eocene and Miocene formations, scattered over those and other adjoining provinces. The discovery of the remains of Paleotherium and other mammalia in some of the upper beds of the calcaire grossier shows that these land animals began to exist before the deposition of the overlying gypseous series had commenced.

Calcaire siliceux.—This compact siliceous limestone extends over a wide area. It resembles a precipitate from the waters of mineral springs, and is often traversed by small empty sinuous cavities. It is, for the most part, devoid of organic remains, but in some places contains freshwater and land species, and never any marine fossils. The siliceous limestone and the calcaire grossier occupy distinct parts of the Paris basin, the one attaining its fullest development in those places where the other is of slight thickness. They also alternate with each other towards the centre of the basin, as at Sergy and Osny; and there are even points where the two rocks are so blended together that portions of each may be seen in hand specimens. Thus, in the same bed, at Triel, we have the compact freshwater limestone, characterized by its Limneæ, mingled with the coarse marine limestone, with its small multilocular shells, or "miliolites," dispersed through it in countless numbers. These microscopic testacea are also accompanied by Cerithia and other shells of the calcaire grossier. It is very extraordinary that in this instance both kinds of sediment must have been thrown down together on the same spot, yet each retains its own peculiar organic remains.

From these facts we may conclude, that while to the north, where the bay was probably open to the sea, a marine limestone was formed, another deposit of freshwater origin was introduced to the southward, or at the head of the bay; for it appears that during the Eocene period, as now, the ocean was to the north, and the continent, where the great lakes existed, to the south. From that southern region we may suppose a body of fresh water to have descended, charged with carbonate of lime and silica, the water being perhaps in sufficient volume to freshen the upper end of the bay. The gypseous series (2. a, Table, [p. 175.]), before described, was once supposed to be entirely subsequent in origin to the two groups, called calcaire grossier and calcaire siliceux. But M. Prevost has pointed out that in some localities they alternate repeatedly with both.

The gypsum, with its associated marl and limestone, is in greatest force towards the centre of the basin, where the calcaire grossier and calcaire siliceux are less fully developed. Hence M. Prevost infers, that while those two principal deposits were gradually in progress, the one towards the north, and the other towards the south, a river descending from the east may have brought down the gypseous and marly sediment.

It must be admitted, as highly probable, that a bay or narrow sea, 180 miles in length, would receive, at more points than one, the waters of the adjoining continent. At the same time, we must be prepared to find that the simultaneous deposition of two or more sets of strata in one basin, some freshwater and others marine, must have produced very complex results. But, in proportion as it is more difficult in these cases to discover any fixed order of superposition in the associated mineral masses, so also is it more easy to explain the manner of their origin, and to reconcile their relations to the agency of known causes. Instead of the successive irruptions and retreats of the sea, and changes in the chemical nature of the fluid, and other speculations of the earlier geologists, we are now simply called upon to imagine a gulf, into one extremity of which the sea entered, and at the other a large river, while other streams may have flowed in at different points, whereby an indefinite number of alternations of marine and freshwater beds would be occasioned.

LOWER EOCENE, FRANCE.

Lits coquilliers (3. a, Table, [p. 175.]).—Below the calcaire grossier are extensive deposits of sand, in the upper parts of which some marine beds, called "lits coquilliers," occur, in which M. d'Archiac has discovered 200 species of shells. Many of these are peculiar, but the larger portion appear to agree with species of the calcaire grossier, so that the line of demarcation usually adopted between the French Lower and Middle Eocene formations, seems not to be very strongly drawn. Sands and plastic clay (3. b, Table, [p. 175.])—At the base of the tertiary system in France are extensive deposits of sands, with occasional beds of clay used for pottery, and called "argile plastique." Fossil oysters (Ostrea bellovacina) abound in some places, and in others there is a mixture of fluviatile shells, such as Cyrena cuneiformis ([fig. 187.] [p. 204.]), Melania inquinata ([fig. 188.]), and others, frequently met with in beds occupying the same position in the valley of the Thames. Layers of lignite also accompany the inferior clays and sands.

Immediately upon the chalk at the bottom of all the tertiary strata there is often a conglomerate or breccia of rolled and angular chalk flints, cemented by siliceous sand. These beds appear to be of littoral origin, and imply the previous emergence of some portions of the chalk, and its waste by denudation.

Fig. 169.

Cardium porulosum. Paris and London basins.

The lower sandy beds of the Paris basin are often called the sands of the Soissonais, from a district so named 50 miles N.E. of Paris. One of the shells of the formation is adduced by M. Deshayes as an example of the changes which certain species underwent in the successive stages of their existence. It seems that different varieties of the Cardium porulosum are characteristic of different formations. In the Lower Eocene of the Soissonais this shell acquires but a small volume, and has many peculiarities, which disappear in the lowest beds of the calcaire grossier. In these the shell attains its full size, and many distinctive characters, which are again modified in the uppermost beds of the calcaire grossier; and these last modifications of form are preserved throughout the whole of the "upper marine" (or Upper Eocene) series.[197-A]

ENGLISH EOCENE FORMATIONS.

The Eocene areas of Hampshire and London are delineated in the map ([fig. 153.] [p. 174.]).

The following table will show the succession of the principal deposits found in our island. The true place of the Bagshot sands, in this series, was never accurately ascertained till Mr. Prestwich published, in 1847, his classification of the English Eocene strata, dividing them into three principal formations, in which the Bagshot sands occupied the central place.[197-B]

Localities.
1. Upper Eocene. Wanting in Great Britain.
2. Middle Eocene { a. Freshwater and fluvio-marine beds. Headon Hill, Isle of Wight; and Hordwell Cliff, Hants.
b. Barton beds. Barton Cliff, Hants.
c. Bagshot and Bracklesham sands and clays. Bagshot Heath, Surrey; Bracklesham Bay, Sussex.
3. Lower Eocene { a. London Clay Proper, and Bognor beds. Highgate Hill, Middlesex; I. of Sheppey; Bognor, Sussex.
b. Mottled and Plastic clays and sands. Newhaven, Sussex; Reading, Berks; Woolwich, Kent.

Fig. 170.

Lymnea longiscata.

Freshwater Eocene strata, Isle of Wight.

Freshwater beds (2. a, Table, [p. 175.]).—In the northern part of the Isle of Wight, beds of marl, clay, and sand, and a friable limestone, containing freshwater shells, are seen, containing shells of the genera Lymnea (see [fig. 170.]), Planorbis, Melanopsis, Cyrena, &c., several of them of the same species as those occurring in the Eocene beds of the Paris basin. Gyrogonites, also, or seed-vessels of Chara, exhibiting a similar specific identity, occur. At Headon Hill, on the western side of the island, where these beds are seen in the sea-cliffs, some of the strata contain a few marine and estuary shells, such as Cytheræa, Corbula, &c., showing a temporary occupation of the area by brackish or salt water, after which the river or a lake seems again to have prevailed. A species of fan-palm, Flabellaria Lamanonis, Brong., like one which characterizes the Parisian Eocene beds, has been recently detected by Dr. Mantell in this formation, in Whitecliff Bay, at the eastern end of the island.

Several of the species of extinct quadrupeds already alluded to as characterizing the gypsum of Montmartre have been discovered by Messrs. Pratt and Fox, in the Isle of Wight, chiefly at Binstead, near Ryde, as Palæotherium magnum, P. medium, P. minus, P. minimum, P. curtum, P. crassum, also Anoplotherium commune, A. secundarium, Dichobune cervinum, and Chæropotamus Cuvieri. In Hordwell cliff, also on the Hampshire coast, several of these species, with other quadrupeds of new genera, such as Paloplotherium, Owen, have been met with; and remains of a remarkable carnivorous genus, Hyænodon. These fossils are accompanied by the bones of Trionyx, and other tortoises, and by two land snakes of the genus Paleryx, Owen, from 3 to 4 feet long, also a species of crocodile, and an alligator. Among other fossils collected by Lady Hastings, Sir Philip Egerton has recognized the well-known gar or bony pike of the American rivers, a ganoid fish of the genus Lepidotus, with its hard shining scales. The shells of Hordwell are similar to those of the freshwater beds of the Isle of Wight, and among them are a few specifically undistinguishable from recent testacea, as Paludina lenta and Helix labyrinthica, the latter discovered by Mr. S. Wood, and identified with an existing N. American helix.

The white and green marls of this freshwater series in Hampshire, and some of the accompanying limestones, often resemble those of France in mineral character and colour in so striking a manner, as to suggest the idea that the sediment was derived from the same region, or produced contemporaneously under very similar geographical circumstances.

Barton beds.—Both in the cliffs of Headon Hill and Hordwell, already mentioned, the freshwater series rests on a mass of pure white sand without fossils, and this is seen in Barton Cliff to overlie a marine deposit, in which 209 species of testacea have been found. More than half of these are peculiar; and, according to Mr. Prestwich, only 11 of them common to the London Clay proper, being in the proportion of only 5 per cent. On the other hand, 70 of them agree with the calcaire grossier shells. As this is the newest purely marine bed of the Eocene series known in England, we might have expected that some of its peculiar fossils would be found to agree with the upper Eocene strata described in the last chapter, and accordingly some identifications have been cited with testacea, both of the Berlin and Belgian strata. It is nearly a century since Brander published, in 1766, an account of the organic remains collected from these cliffs, and his excellent figures of the shells then deposited in the British Museum are justly admired by conchologists for their accuracy.

Bagshot Sands (2. c, Table, [p. 197.]).—These beds, consisting chiefly of siliceous sand, occupy extensive tracts round Bagshot, in Surrey, and in the New Forest, Hampshire. They succeed next in chronological order, and may be separated into three divisions, the upper and lower consisting of light yellow sands, and the central of dark green sands and brown clays, the whole reposing on the London clay proper.[199-A] Although the Bagshot beds are usually devoid of fossils, they contain marine shells in some places, among which Venericardia planicosta (see [fig. 171.]) is abundant, with Turritella sulcifera and Nummulites lævigatus. (See [fig. 174.] [p. 200.])

Fig. 171.

Venericardia planicosta, Lamck.

Cardita planicosta, Deshayes.

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.

Fig. 172.

Prolonged premaxillary bone or "sword" of a fossil sword-fish (Cælorhynchus). Bracklesham. Dixon's Fossils of Sussex, pl. 8.

Fig. 173.

Dental plates of Myliobates Edwardsi. Bracklesham Bay. Ibid. pl. 8.

Fig. 174.

Nummulites (Nummularia) lævigatus. Bracklesham. Ibid. pl. 8.

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.

Fig. 175.

Nipadites ellipticus. Bow. Fossil palm of Sheppey.

The contiguity of land may be inferred not only from these vegetable productions, but also from the teeth and bones of crocodiles and turtles, since these creatures, as Mr. Conybeare has remarked, must have resorted to some shore to lay their eggs. Of turtles there were numerous species referred to extinct genera, and, for the most part, not equal in size to the largest living tropical turtles. A snake, which must have been 13 feet long, of the genus Palæophis before mentioned, has also been described by Mr. Owen from Sheppey, of a different species from that of Bracklesham. A true crocodile, also, Crocodilus toliapicus, and another Saurian more nearly allied to the gravial, accompany the above fossils. A bird allied to the vultures, and a quadruped of the new genus Hyracotherium, allied to the Hyrax, Hog, and Chæropotamus, are also among the additions made of late years to the palæontology of this division.

FOSSIL SHELLS OF THE LONDON CLAY.

Fig. 176. Mitra scabra.

Fig. 177. Rostellaria macroptera, Sow. One-third of nat. size.

Fig. 178. Crassatella sulcata.

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.])

Fig. 179.

Nautilus centralis.

Fig. 180.

Voluta athleta.

Fig. 181.

Terebellum fusiforme.

Fig. 182.

Aturia zigzag. Bronn. Syn. Nautilus zigzag. Sow. London clay. Sheppey.

Fig. 183.

Belosepia sepiodea, De Blainv. London clay. Sheppey.

The above shells are accompanied by a sword-fish (Tetrapterus priscus, Agassiz), about 8 feet long, and a saw-fish (Pristis bisulcatus, Ag.), about 10 feet in length; genera now foreign to the British seas. On the whole, no less than 50 species of fish have been described by M. Agassiz from these beds in Sheppey, and they indicate, in his opinion, a warm climate.

Fig. 184.

Molar of monkey (Macacus).

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.

Fig. 185.

Molar tooth and part of jaw of opossum. From Kyson.[203-A]

Fig. 186.

Molars of insectivorous bats, twice nat. size. From Kyson, Suffolk.

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.

Fig. 187.

Cyrena cuneiformis, Min. Con. Natural size.

Fig. 188.

Melania inquinata, Des. Nat. size.

Syn. Cerithium melanoides, Min. Con.

With us as in France, clay of this formation is used in some places, as near Poole in Dorsetshire, for pottery; and hence the name of plastic clay was adopted for the group by Mr. T. Webster. Lignite also is associated with it in some spots, as in the Paris basin.

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.

Fig. 189.

Nummulites. Peyrehorade, Pyrenees.

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.

Fig. 190.

1. Sand, marl, &c., with numerous fossils. } Eocene.
2. White or rotten limestone, with Zeuglodon.
3. Orbitoidal, or so called nummulitic limestone.

4. Overlying formation of sand and clay without fossils.		 Age unknown.

The lowest set of strata, No. 1., having a thickness of more than 100 feet, comprise marly beds, in which the Ostrea sellæformis occurs, a shell ranging from Alabama to Virginia, and being a representative form of the Ostrea flabellula of the Eocene group of Europe. In others beds of No. 1., two European shells, Cardita planicosta, before mentioned, and Solarium canaliculatum are found, with a great many other species peculiar to America. Numerous corals, also, and the remains of placoid fish and of rays occur, and the "swords," as they are called, of sword fishes, all bearing a great generic likeness to those of the Eocene strata of England and France.

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]

Zeuglodon cetoides, Owen.
Basilosaurus, Harlan.

Fig. 191. Molar tooth, natural size.

Fig. 192. Vertebra, reduced.

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.

Divisions of the cretaceous series in North-Western Europe — Upper cretaceous strata — Maestricht beds — Chalk of Faxoe — White chalk — Characteristic fossils — Extinct cephalopoda — Sponges and corals of the chalk — Signs of open and deep sea — Wide area of white chalk — Its origin from corals and shells — Single pebbles in chalk — Siliceous sandstone in Germany contemporaneous with white chalk — Upper greensand and gault — Lower cretaceous strata — Atherfield section, Isle of Wight — Chalk of South of Europe — Hippurite limestone — Cretaceous Flora — Chalk of United States.

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]:

Upper Cretaceous.
1. Maestricht beds and Faxoe limestone.
2. Upper white chalk, with flints.
3. Lower white chalk, without flints, passing downwards into chalk marl, which is slightly argillaceous.
4. Upper greensand.
5. Gault.
Lower Cretaceous.
6. Lower greensand—Ironsand, clay, and occasional beds of limestone (Kentish rag).

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.

Fig. 193.

Section from Hertfordshire, in England, to Sena, in France.

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.

Fig. 194.

Portion of Baculites Faujasii. Maestricht and Faxoe beds and white chalk.

Fig. 195.

Portion of Baculites anceps. Maestricht and Faxoe beds and white chalk.

Fig. 196.

Fig. 197.

Maestricht, Faxoe, and white chalk.

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.]).

Fig. 198.

Terebratula plicatilis, dorsal view. Upper white chalk.

Fig. 199.

Terebratula plicatilis, side view.

Fig. 200.

Terebratula pumilus. (Magas pumilus, Sow.) Upper white chalk.

Fig. 201.

Terebratula carnea. Upper white chalk.

Fig. 202.

Ostrea vesicularis. Gryphæa globosa, Min. Con. Upper chalk and upper greensand.

Fig. 203.

Pecten 5-costatus. White chalk, upper and lower greensands.

Fig. 204.

Ostrea carinata. Chalk marl, upper and lower greensands.

Fig. 205.

Crania Parisiensis, inferior or attached valve. Upper white chalk.

Fig. 206.

Plagiostoma Hoperi, Sow. Syn. Lima Hoperi. White chalk and upper greensand.

Fig. 207.

Plagiostoma spinosum, Sow. Syn. Spondylus spinosus. Upper white chalk.

Among the rest, no form marks the cretaceous era in Europe, America, and India, in a more striking manner than the extinct genus Inoceramus (Catillus of Lamk.), the shells of which are distinguished by a fibrous texture, and are often met with in fragments, having, probably, been extremely friable.

Fig. 208.

Inoceramus Lamarckii.
Syn. Catillus Lamarckii.

White Chalk (Dixon's Geol. Sussex, Tab. 28. fig. 29.)

Fig. 209.

Eschara disticha.

White chalk.

A branching sponge in a flint, from the white chalk. From the collection of Mr. Bowerbank.

With these mollusca are many corals ([figs. 209], [210], [211.]) and sea urchins ([fig. 212.]), which are alike marine, and, for the most part, indicative of a deep sea. They are dispersed indifferently through the soft chalk, and hard flint, and some of the flinty nodules owe their irregular forms to inclosed zoophytes, as in the specimen represented in [fig. 211.], where the hollows in the exterior are caused by the branches of a sponge seen on breaking open the flint, [fig. 210.]

Fig. 212.

Ananchytes ovata. White chalk, upper and lower.

Of the singular family called Rudistes, by Lamarck, hereafter to be mentioned, as extremely characteristic of the chalk of Southern Europe, a single representative only ([fig. 213.]) has been discovered in the white chalk of England.

Hippurites Mortoni, Mantell. Houghton, Sussex. White chalk. Diameter one seventh of nat. size.

On the side where the shell is thinnest, there is one external furrow and corresponding internal ridge, a, b. [figs. 213], [214.]; but they are usually less prominent than in these figures. This species has been referred to Hippurites, but does not, I believe, fully agree in character with that genus. I have never seen the opercular piece, or valve, as it is called by those conchologists who regard the Rudistes as bivalve mollusca. The specimen above figured was discovered by the late Mr. Dixon.

The remains of fishes of the Upper Cretaceous formations consist chiefly of teeth of the shark family of genera, in part common to the tertiary, and partly distinct. But we meet with no bones of land animals, nor any terrestrial or fluviatile shells, nor any plants, except sea weeds, and here and there a piece of drift wood. All the appearances concur in leading us to conclude that the white chalk was the product of an open sea of considerable depth.

The existence of turtles and oviparous saurians, and of a Pterodactyl or winged-lizard, found in the white chalk of Maidstone, implies, no doubt, some neighbouring land; but a few small islets in mid-ocean, like Ascension, so much frequented by migratory droves of turtles, might perhaps have afforded the required retreat where these creatures might lay their eggs in the sand, or from which the flying species may have been blown out to sea. Of the vegetation of such islands we have scarcely any indication, but it consisted partly of cycadeous plants; for a fragment of one of these was found by Capt. Ibbetson in the chalk marl of the Isle of Wight, and is referred by A. Brongniart to Clathraria Lyellii, Mantell, a species common to the antecedent Wealden period.

Geographical extent and origin of the While Chalk.—The area over which the white chalk preserves a nearly homogeneous aspect is so vast, that the earlier geologists despaired of discovering any analogous deposits of recent date. Pure chalk, of nearly uniform aspect and composition, is met with in a north-west and south-east direction, from the north of Ireland to the Crimea, a distance of about 1140 geographical miles; and in an opposite direction it extends from the south of Sweden to the south of Bordeaux, a distance of about 840 geographical miles. In Southern Russia, according to Sir R. Murchison, it is sometimes 600 feet thick, and retains the same mineral character as in France and England, with the same fossils, including Inoceramus Cuvieri, Belemnites mucronatus, and Ostrea vesicularis.

But it would be an error to imagine, that the chalk was ever spread out continuously over the whole of the space comprised within these limits, although it prevailed in greater or less thickness over large portions of that area. On turning to those regions of the Pacific where coral reefs abound, we find some archipelagoes of lagoon islands, such as that of the Dangerous Archipelago, for instance, and that of Radack, with several adjoining groups, which are from 1100 to 1200 miles in length, and 300 or 400 miles broad; and the space to which Flinders proposed to give the name of the Corralline Sea is still larger; for it is bounded on the east by the Australian barrier—all formed of coral rock,—on the west by New Caledonia, and on the north by the reefs of Louisiade. Although the islands in these areas may be thinly sown, the mud of the decomposing zoophytes may be scattered far and wide by oceanic currents. That this mud would resemble chalk I have already hinted when speaking of the Faxoe limestone, [p. 211.]; and it was also remarked in an early part of this volume, that some even of that chalk which appears to an ordinary observer quite destitute of organic remains, is nevertheless, when seen under the microscope, full of fragments of corals and sponges; together with the valves of entomostraca, the shells of foraminifera, and still more minute infusoria.[215-A] (See [p. 26.])

Now it had been often suspected, before these discoveries, that white chalk might be of animal origin, even where every trace of organic structure has vanished. This bold idea was partly founded on the fact, that the chalk consisted of pure carbonate of lime, such as would result from the decomposition of testacea, echini, and corals; and partly on the passage observable between these fossils when half decomposed and chalk. But this conjecture seemed to many naturalists quite vague and visionary, until its probability was strengthened by new evidence brought to light by modern geologists.

We learn from Lieutenant Nelson, that, in the Bermuda Islands, there are several basins or lagoons almost surrounded and enclosed by reefs of coral. At the bottom of these lagoons a soft white calcareous mud is formed by the decomposition of Eschara, Flustra, Cellepora, and other corallines. This mud, when dried, is undistinguishable from common white earthy chalk; and some portions of it, presented to the Museum of the Geological Society of London, might, after full examination, be mistaken for ancient chalk, but for the labels attached to them. About the same time Mr. C. Darwin observed similar facts in the coral islands of the Pacific; and came also to the opinion, that much of the soft white mud found at the bottom of the sea near coral reefs has passed through the bodies of worms, by which the stony masses of coral are everywhere bored; and other portions through the intestines of fishes; for certain gregarious fishes of the genus Sparus are visible through the clear water, browsing quietly, in great numbers, on living corals, like grazing herds of graminivorous quadrupeds. On opening their bodies, Mr. Darwin found their intestines filled with impure chalk. This circumstance is the more in point, when we recollect how the fossilist was formerly puzzled by meeting, in chalk, with certain bodies, called cones of the larch, which were afterwards recognized by Dr. Buckland to be the excrement of fish.[216-A] These spiral coprolites (see figures), like the scales and bones of fossil fish in the chalk, are composed chiefly of phosphate of lime.

Coprolites of fish called Iulo-eido-copri, from the chalk.

Mr. Dana, when describing the elevated coral reef of Oahu, in the Sandwich Islands, says, that some varieties of the rock consist of aggregated shells, imbedded in a compact calcareous base as firm in texture as any secondary limestone; while others are like chalk, having its colour, its earthy fracture, its soft homogeneous texture, and being an equally good writing material. The same author describes, in many growing coral reefs, a similar formation of modern chalk, undistinguishable from the ancient.[216-B] The extension over a wide submarine area of the calcareous matrix of the chalk, as well as of the imbedded fossils, would take place the more readily, in consequence of the low specific gravity of the shells of mollusca and zoophytes, when compared with ordinary sand and mineral matter. The mud also derived from their decomposition would be much lighter than argillaceous and other inorganic mud, and very easily transported by currents, especially in salt water.

Single pebbles in chalk.—The general absence of sand and pebbles in the white chalk has been already mentioned; but the occurrence here and there, in the south-east of England, of a few isolated pebbles of quartz and green schist, some of them 2 or 3 inches in diameter, has justly excited much wonder. If these had been carried to the spots where we now find them by waves or currents from the lands once bordering the cretaceous sea, how happened it that no sand or mud were transported thither at the same time? We cannot conceive such rounded stones to have been drifted like erratic blocks by ice[217-A], for that would imply a cold climate in the Cretaceous period; a supposition inconsistent with the luxuriant growth of large chambered univalves, numerous corals, and many fish, and other fossils of tropical forms.

Now in Keeling Island, one of those detached masses of coral which rise up in the wide Pacific, Captain Ross found a single fragment of greenstone, where every other particle of matter was calcareous; and Mr. Darwin concludes that it must have come there entangled in the roots of a large tree. He reminds us that Chamisso, the distinguished naturalist who accompanied Kotzebue, affirms, that the inhabitants of the Radack archipelago, a group of lagoon islands, in the midst of the Pacific, obtained stones for sharpening their instruments by searching the roots of trees which are cast up on the beach.[217-B]

It may perhaps be objected, that a similar mode of transport cannot have happened in the cretaceous sea, because fossil wood is very rare in the chalk. Nevertheless wood is sometimes met with, and in the same parts of the chalk where the pebbles are found, both in soft stone and in a silicified state in flints. In these cases it has often every appearance of having been floated from a distance, being usually perforated by boring-shells, such as the Teredo and Fistulana.[217-C]

The only other mode of transport which suggests itself is sea-weed. Dr. Beck informs me, that in the Lym-Fiord, in Jutland, the Fucus vesiculosus, often called kelp, sometimes grows to the height of 10 feet, and the branches rising from a single root form a cluster several feet in diameter. When the bladders are distended, the plant becomes so buoyant as to float up loose stones several inches in diameter, and these are often thrown by the waves high up on the beach. The Fucus giganteus of Solander, so common in Terra del Fuego, is said by Captain Cook to attain the length of 360 feet, although the stem is not much thicker than a man's thumb. It is often met with floating at sea, with shells attached, several hundred miles from the spots where it grew. Some of these plants, says Mr. Darwin, were found adhering to large loose stones in the inland channels of Terra del Fuego, during the voyage of the Beagle in 1834; and that so firmly, that the stones were drawn up from the bottom into the boat, although so heavy that they could scarcely be lifted in by one person. Some fossil sea-weeds have been found in the Cretaceous formation, but none, as yet, of large size.

But we must not imagine that because pebbles are so rare in the white chalk of England and France there are no proofs of sand, shingle, and clay having been accumulated contemporaneously even in the European seas. The siliceous sandstone, called "upper quader" by the Germans, overlies white argillaceous chalk, or "pläner-kalk," a deposit resembling in composition and organic remains the chalk marl of the English series. This sandstone contains as many fossil shells common to our white chalk as could be expected in a sea-bottom formed of such different materials. It sometimes attains a thickness of 600 feet, and by its jointed structure and vertical precipices, plays a conspicuous part in the picturesque scenery of Saxon Switzerland, near Dresden.

Upper greensand (4. Tab. [p. 209.]).—The lower chalk without flints passes gradually downwards, in the south of England, into an argillaceous limestone, "the chalk marl," already alluded to, in which ammonites and other cephalopoda, so rare in the higher parts of the series, appear. This marly deposit passes in its turn into beds containing green particles of a chloritic mineral, called the upper greensand. In parts of Surrey calcareous matter is largely intermixed, forming a stone called firestone. In the cliffs of the southern coast of the Isle of Wight, this upper greensand is 100 feet thick, and contains bands of siliceous limestone and calcareous sandstone with nodules of chert.

Fossils of the Upper Greensand.

Fig. 219.

a. Terebratula lyra. } Upper greensand.
b. Same, seen in profile. France.

Fig. 220. Ammonites Rhotomagensis.
Upper greensand.

Fig. 221.

Hamites spiniger (Fitton); near Folkstone. Gault.

Gault.—The lowest member of the upper Cretaceous group, usually about 100 feet thick in the S.E. of England, is provincially termed Gault. It consists of a dark blue marl, sometimes intermixed with greensand. Many peculiar forms of cephalopoda, such as the Hamite ([fig. 221.]) and Scaphite, with other fossils, characterize this formation, which, small as is its thickness, can be traced by its organic remains to distant parts of Europe, as, for example, to the Alps.

The phosphate of lime, found lately near Farnham, in Surrey, in such abundance as to be used largely by the agriculturist for fertilizing soils, occurs exclusively, according to Mr. R. A. C. Austen, in the upper greensand and gault. It is doubtless of animal origin, and partly coprolitic, probably derived from the excrement of fish.

LOWER CRETACEOUS DIVISION. (No. 6. Tab. [p. 209.])

That part of the Cretaceous series which is older than the Gault has been commonly called the Lower Greensand. The greater number of its fossils are specifically distinct from those of the upper cretaceous system. Dr. Fitton, to whom we are indebted for an excellent monograph on this formation as developed in England, gives the following as the succession of rocks seen in parts of Kent.

No. 1. Sand, white, yellowish, or ferruginous, with concretions of limestone and chert 70 feet.
2. Sand with green matter 70 to 100 feet.
3. Calcareous stone, called Kentish rag 60 to 80 feet.

In his detailed description of the fine section displayed at Atherfield, in the south of the Isle of Wight, we find the limestone wholly wanting; in fact, the variations in the mineral composition of this group, even in contiguous districts, is very great; and on comparing the Atherfield beds with corresponding strata at Hythe in Kent, distant 95 miles, the whole series has lost half its thickness, and presents a very dissimilar aspect.[219-A]

On the other hand, Professor E. Forbes has shown that when the sixty-three strata at Atherfield are severally examined, the total thickness of which he gives as 843 feet, there are some fossils which range through the whole series, others which are peculiar to particular divisions. As a proof that all belong chronologically to one system, he states that whenever similar conditions are repeated in overlying strata the same species reappear. Changes of depth, or of the mineral nature of the bottom, the presence or absence of lime or of peroxide of iron, the occurrence of a muddy, or a sandy, or a gravelly bottom, are marked by the banishment of certain species and the predominance of others. But these differences of conditions being mineral, chemical, and local in their nature, have nothing to do with the extinction, throughout a large area, of certain animals or plants. The rule laid down by this eminent naturalist for enabling us to test the arrival of a new state of things in the animate world, is the representation by new and different species of corresponding genera of mollusca or other beings. When the forms proper to loose sand or soft clay, or a stony or calcareous bottom, or a moderate or a great depth of water, recur with all the same species, the interval of time has been, geologically speaking, small, however dense the mass of matter accumulated. But if, the genera remaining the same, the species are changed, we have entered upon a new period; and no similarity of climate, or of geographical and local conditions, can then recall the old species which a long series of destructive causes in the animate and inanimate world has gradually annihilated. On passing from the lower greensand to the gault, we suddenly reach one of these new epochs, scarcely any of the fossil species being common to the lower and upper cretaceous systems, a break in the chain implying no doubt many missing links in the series of geological monuments which we may some day be able to supply.

One of the largest and most abundant shells in the lowest strata of the lower greensand, as displayed in the Atherfield section, is the large Perna mulleti of which a reduced figure is here given ([fig. 222.]).

Fig. 222.

Perna mulleti. Desh. in Leym.

In the south of England, during the accumulation of the lower greensand above described, the bed of the sea appears to have been continually sinking, from the commencement of the period, when the freshwater Wealden beds were submerged, to the deposition of those strata on which the gault immediately reposes.

Pebbles of quartzose sandstone, jasper, and flinty slate, together with grains of chlorite and mica, speak plainly of the nature of the pre-existing rocks, from the wearing down of which the greensand beds were derived. The land, consisting of such rocks, was doubtless submerged before the origin of the white chalk, as corals can only multiply in the clear waters of the sea in spaces to which no mud or sand are conveyed by currents.

HIPPURITE LIMESTONE.

Difference between the chalk of the north and south of Europe.—By the aid of the three tests of relative age, namely, superposition, mineral character, and fossils, the geologist has been enabled to refer to the same Cretaceous period certain rocks in the north and south of Europe, which differ greatly, both in their fossil contents and in their mineral composition and structure.

If we attempt to trace the cretaceous deposits from England and France to the countries bordering the Mediterranean, we perceive, in the first place, that the chalk and Greensand in the neighbourhood of London and Paris form one great continuous mass, the Straits of Dover being a trifling interruption, a mere valley with chalk cliffs on both sides. We then observe that the main body of the chalk which surrounds Paris stretches from Tours to near Poitiers (see the annexed map, [fig. 223.], in which the shaded part represents chalk).

Fig. 223.

Between Poitiers and La Rochelle, the space marked A on the map separates two regions of chalk. This space is occupied by the Oolite and certain other formations older than the Chalk, and has been supposed by M. E. de Beaumont to have formed an island in the cretaceous sea. South of this space we again meet with a formation which we at once recognize by its mineral character to be chalk, although there are some places where the rock becomes oolitic. The fossils are, upon the whole, very similar; especially certain species of the genera Spatangus, Ananchytes, Cidarites, Nucula, Ostrea, Gryphæa (Exogyra), Pecten, Plagiostoma (Lima), Trigonia, Catillus, (Inoceramus), and Terebratula.[221-A] But Ammonites, as M. d'Archiac observes, of which so many species are met with in the chalk of the north of France, are scarcely ever found in the southern region; while the genera Hamite, Turrilite, and Scaphite, and perhaps Belemnite, are entirely wanting.

On the other hand, certain forms are common in the south which are rare or wholly unknown in the north of France. Among these may be mentioned many Hippurites, Sphærulites, and other members of that great family of mollusca called Rudistes by Lamarck, to which nothing analogous has been discovered in the living creation, but which is quite characteristic of rocks of the Cretaceous era in the south of France, Spain, Sicily, Greece, and other countries bordering the Mediterranean.

Fig. 224.

White chalk of France.

Fig. 225.

Radiolites foliaceus, D'Orb. Syn. Sphærulites agariciformis, Blainv. White chalk of France.

Fig. 226.

Hippurites organisans, Desmoulins. Upper chalk:—chalk marl of Pyrenees?[222-A]

The species called Hippurites organisans ([fig. 226.]) is more abundant than any other in the south of Europe; and the geologist should make himself well acquainted with the cast d, which is far more common in many compact marbles of the upper cretaceous period than the shell itself, which has often wholly disappeared. The flutings, or smooth, rounded, longitudinal ribs, representing the form of the interior, are wholly unlike the hippurite itself, and in some individuals, which attain a great size and length, are very conspicuous.

Between the region of chalk last mentioned in which Perigueux is situated, and the Pyrenees, the space B intervenes. (See Map, [p. 221.]) Here the tertiary strata cover, and for the most part conceal, the cretaceous rocks, except in some spots where they have been laid open by the denudation of newer formations. In these places they are seen still preserving the form of a white chalky rock, which is charged in part with grains of green sand. Even as far south as Tercis, on the Adour, near Dax, where I examined them in 1828, the cretaceous rocks retain this character. In that region M. Grateloup has found in them Ananchytes ovata ([fig. 212.]), and other fossils of the English chalk, together with Hippurites.

FLORA OF THE CRETACEOUS PERIOD.

Although the fossil plants of the Cretaceous era at present known are few in number, the rocks being principally marine, they suffice, according to M. Ad. Brongniart, to show a transition character between the vegetation of the secondary and that of the tertiary formations. The tertiary strata, when compared to the older rocks, are marked by the predominance of Exogens, which now constitute three-fourths of the living plants of the globe.[223-A]

These exogens are wanting in the secondary strata generally, but in the Cretaceous period they equal in number the Gymnogens (Coniferæ and Cycadeæ) which abounded so much in the preceding Oolitic period, and disappeared before the Eocene rocks were formed.[223-B] The discovery of a tree-fern in the ferruginous sands of the Lower Cretaceous group of the department of Ardennes in France is one of many signs of the contrast of the flora, and doubtless of the climate, of this era with that of the Pliocene and Modern periods.

CRETACEOUS ROCKS IN THE UNITED STATES.

If we pass to the American continent, we find in the state of New Jersey a series of sandy and argillaceous beds wholly unlike our Upper Cretaceous system; which we can, nevertheless, recognize as referable, paleontologically, to the same division.

That they were about the same age generally as the European chalk and greensand, was the conclusion to which Dr. Morton and Mr. Conrad came after their investigation of the fossils in 1834. The strata consist chiefly of greensand and green marl, with an overlying coralline limestone of a pale yellow colour, and the fossils, on the whole, agree most nearly with those of the upper European series, from the Maestricht beds to the gault inclusive. I collected sixty shells from the New Jersey deposits in 1841; five of which were identical with European species—Ostrea larva, O. vesicularis, Gryphæa costata, Pecten quinque-costatus, Belemnites mucronatus. As some of these have the greatest vertical range in Europe, they might be expected more than any others to recur in distant parts of the globe. Even where the species are different, the generic forms, such as the Baculite and certain sections of Ammonites, as also the Inoceramus (see above, [fig. 208.]) and other bivalves, have a decidedly cretaceous aspect. Fifteen out of the sixty shells above alluded to, were regarded by Professor Forbes as good geographical representatives of well-known cretaceous fossils of Europe. The correspondence, therefore, is not small, when we reflect that the part of the United States where these strata occur is between 3000 and 4000 miles distant from the chalk of Central and Northern Europe, and that there is a difference of ten degrees in the latitude of the places compared on opposite sides of the Atlantic.[224-A]

Fish of the genera Lamna, Galeus, and Carcharias are common to New Jersey and the European cretaceous rocks. So also is the genus Mosasaurus among reptiles, and Pliosaurus (Owen), another saurian likewise obtained from the English chalk. From New Jersey the cretaceous formation extends southwards to North Carolina, Georgia, and Alabama, cropping out at intervals from beneath the tertiary strata, between the Appalachian Mountains and the Atlantic. They then sweep round the southern extremity of that chain, and stretch northwards again to Tennessee and Kentucky. They have also been traced far up the valley of the Missouri 275 English miles above its mouth, to the neighbourhood of Fort Leavenworth; and southwards to Texas, according to the observations of Ferdinand Römer; so that already the area which they are ascertained to occupy in North America may perhaps equal their extent in Europe. So little do they resemble mineralogically the European white chalk, that limestone in North America is, upon the whole, an exception to the rule; and, even in Alabama, where I saw a calcareous member of this group, the marlstones are much more like the English and French Lias than any other secondary deposit of the Old World.

At the base of the system in Alabama I found dense masses of shingle, perfectly loose and unconsolidated, derived from the waste of paleozoic (or carboniferous) rocks, a mass in no way distinguishable, except by its position, from ordinary alluvium, but covered with marls abounding in Inocerami.

In Texas, according to F. Römer, the chalk assumes a new lithological type, a large portion of it consisting of hard siliceous limestone, but the organic remains leaving no doubt in regard to its age.

In South America the cretaceous strata have been discovered in Columbia, as at Bogota and elsewhere, containing Ammonites, Hamites, Inocerami, and other characteristic shells.[225-A]

In the South of India, also, at Pondicherry, Verdachellum, and Trinconopoly, Messrs. Kaye and Egerton have collected fossils belonging to the cretaceous system. Taken in connection with those from the United States they prove, says Prof. E. Forbes, that those powerful causes which stamped a peculiar character on the forms of marine animal life at this period, exerted their full intensity through the Indian, European, and American seas.[225-B] Here, as in North and South America, the cretaceous character can be recognized even where there is no specific identity in the fossils; and the same may be said of the organic type of those rocks in Europe and India which succeed next in the ascending and descending order, the Eocene and the Oolitic.