3. The _Aptien_ (or Greensand) consists generally of marls and clay. In France it is found in the department of Vaucluse, at Apt (whence the name Aptien), in the department of the Yonne, and in the Haute-Marne.

Fossils, _Ancyloceras Matheronia.n.u.s_, _Ostrea aquila_, and _Plicatula placunea_. These beds consist here of greyish clay, which is used for making tiles; there of bluish argillaceous limestone, in black or brownish flags. In the Isle of Wight it becomes a fine sandstone, greyish and slightly argillaceous, which at Havre, and in some parts of the country of Bray, become well-developed ferruginous sandstones.

[Ill.u.s.tration: Fig. 143.--Cypris spinigera.]

[Ill.u.s.tration: Fig. 144.--Cypris Valdensis.]

We have noted that the Lower Neocomian formation, although a marine deposit, is in some respects the equivalent of the _Weald Clay_, a fresh-water formation of considerable importance on account of its fossils. We have seen that it was either formed at the mouth of a great river, or the river was sufficiently powerful for the fresh-water current to be carried out to sea, carrying with it some animals, forming a fluviatile, or lacustrine fauna, on a small scale. These were small Crustaceans of the genus _Cypris_, with some molluscous Gasteropoda of the genera _Melania_, _Paludina_, and acephalous Mollusca of the five genera _Cyrena_, _Unio_, _Mytilus_, _Cyclas_, and _Ostrea_. Of these, _Cypris spinigera_ (Fig. 143) and _Cypris Valdensis_ (Fig. 144) may be considered as among the most characteristic fossils of this local fauna.

The Cretaceous series is not interesting for its fossils alone; it presents also an interesting subject for study in a mineralogical point of view. The white Chalk, examined under the microscope by Ehrenberg, shows a curious globiform structure. The green part of its sandstone and limestone const.i.tutes very singular compounds. According to the result of Berthier's a.n.a.lysis, we must consider them as silicates of iron. The iron shows itself here not in beds, as in the Jura.s.sic rocks, but in ma.s.ses, in a species of pocket in the Orgonian beds. They are usually hydrates in the state of hemat.i.tes, accompanied by quant.i.ties of ochre so abundant that they are frequently unworkable. In the south of France these veins were mined to a great depth by the ancient monks, who were the metallurgists of their age. But for the artist the important Orgonian beds possess a special interest; their admirable vertical fractures, their erect perpendicular peaks, each surpa.s.sing the other in boldness, form his finest studies. In the Var, the defiles of Vesubia, of the Esteron, and Tinea, are jammed up between walls of peaks, for many hundreds of yards, between which there is scarcely room for a narrow road by the side of the roaring torrent. "In the Drome," says Fournet, "the entrance to the beautiful valley of the Vercors is closed during a part of the year, because, in order to enter, it is necessary to cross the two gullies, the _Great_ and _Little Goulet_, through which the waters escape from the valley. Even during the dry season, he who would enter the gorge must take a foot-bath.

"This state of things could not last; and in 1848 it was curious to see miners suspended on the sides of one of these lateral precipices, some 450 feet above the torrent, and about an equal distance below the summit of the Chalk. There they began to excavate cavities or niches in the face of the rock, all placed on the same level, and successively enlarged. These were united together in such a manner as to form a road practicable for carriages; now through a gallery, now covered by a corbelling, to look over which affords a succession of surprises to the traveller.

"This is not all," adds M. Fournet: "he who traverses the high plateaux of the country finds at every step deep diggings in the soil, designated pits or _scialets_, the oldest of which have their sides clothed with a curious vegetation, in which the _Aucolin_ predominates; shelter is found in these pits from the cutting winds which rage so furiously in these elevated regions. Others form a kind of cavern, in which a temperature obtains sufficient to freeze water even in the middle of summer. These cavities form natural _glaciers_, which we again find upon some of the table-lands of the Jura.

"The cracks and creva.s.ses of the limestone receive the waters produced by falling rain and melted snow; true to the laws of all fluid bodies, they filter through the rocks until they reach the lower and impervious marly beds, where they form sheets of water, which in course of time find some outlet through which they discharge themselves. In this manner subterranean galleries, sometimes of great extent, are formed, in which are a.s.sembled all the marvels which crumbling stalact.i.tes, stalagmites, placid lakes, and headlong torrents can produce; finally, these waters, forcing their way through the external orifices, give rise to those fine cascades which, with the first gushing torrent, form an actual river."

The _Albien_ of Alc. D'Orbigny, which Lyell considers to be the equivalent of the _Gault_, French authors treat as the "_glauconie_"

formation, the name being drawn from a rock composed of chalk with greenish grains of _glauconite_, or silicate of iron, which is often mixed with the limestone of this formation. The fossils by which it is identified are very varied. Among its numerous types, we find Crustaceans belonging to the genera _Arcania_ and _Corystes_; many new Mollusca, _Buccinum_, _Solen_, _Pterodonta_, _Voluta_, _Chama_, &c.; great numbers of molluscous Brachiopods, forming highly-developed submarine strata; some Echinoderms, unknown up to this period, and especially a great number of Zoophytes; some Foraminifera, and many Polyzoa (Bryozoa). The glauconitic formation consists of two groups of strata: the _Gault_ Clay and the _glauconitic_ chalk, or Upper Greensand and Chloritic Marl.

UPPER CRETACEOUS PERIOD.

During this phase of the terrestrial evolutions, the continents, to judge from the fossilised wood which we meet with in the rocks which now represent it, would be covered with a very rich vegetation, nearly identical, indeed, with that which we have described in the preceding sub-period; according to Adolphe Brongniart, the "age of angiosperms"

had fairly set in; the Cretaceous flora displays, he considers, a transitional character from the Secondary to the Tertiary vegetation; that the line between the gymnosperms, or naked-seeded plants, and the angiosperms, having their seeds enclosed in seed-vessels, runs between the Upper and Lower Cretaceous formations. "We can now affirm," says Lyell, "that these Aix-la-Chapelle plants, called Credneria, flourished before the rich reptilian fauna of the secondary rocks had ceased to exist. The Ichthyosaurus, Pterodactyle, and Mosasaurus were of coeval date with the oak, the walnut, and the fig."[80]

[80] Lyell's "Elements of Geology," p. 333.

The terrestrial fauna, consisting of some new Reptiles haunting the banks of rivers, and Birds of the genus Snipe, have certainly only reached us in small numbers. The remains of the marine fauna are, on the contrary, sufficiently numerous and well preserved to give us a great idea of its riches, and to enable us to a.s.sign to it a characteristic facies.

The sea of the Upper Cretaceous period bristled with numerous submarine reefs, occupying a vast extent of its bed--reefs formed of Rudistes (Lamarck), and of immense quant.i.ties of various kinds of corals which are everywhere a.s.sociated with them. The Polyps, in short, attain here one of the princ.i.p.al epochs of their existence, and present a remarkable development of forms; the same occurs with the Polyzoa (Bryozoa) and Amorphozoa; while, on the contrary, the reign of the Cephalopods seems to end. Beautiful types of these ancient reefs have been revealed to us, and we discover that they have been formed under the influence of submarine currents, which acc.u.mulated ma.s.ses of these animals at certain points. Nothing is more curious than this a.s.semblage of _Rudistes_--still standing erect, isolated or in groups--as may be seen, for instance, at the summit of the mountains of the _Cornes_ in the Corbieres, upon the banks of the pond of Berre in Provence, and in the environs of Martigues, at La Cadiere, at Figuieres, and particularly above Beausset, near Toulon.

"It seems," says Alcide D'Orbigny, "as if the sea had retired in order to show us, still intact, the submarine fauna of this period, such as it was when in life. There are here enormous groups of _Hippurites_ in their places, surrounded by Polyps, Echinoderms, and Molluscs, which lived in union in these animal colonies, a.n.a.logous to those which still exist in the coral-reefs of the Antilles and Oceania. In order that these groups should have been preserved intact, they must first have been covered suddenly by sediment, which, being removed by the action of the atmosphere, reveals to us, in their most secret details, this Nature of the past."

In the Jura.s.sic period we have already met with these isles or reefs formed by the acc.u.mulation of Coral and other Zoophytes; they even const.i.tuted, at that period, an entire formation called the _Coral-rag_.

The same phenomenon, reproduced in the Cretaceous seas, gave rise to similar calcareous formations. We need not repeat what we have said already on this subject when describing the Jura.s.sic period. The coral or madrepore isles of the Jura.s.sic epoch and the reefs of Rudistes and Hippurites of the Cretaceous period have the same origin, and the _atolls_ of Oceania are reproductions in our own day of precisely similar phenomena.

The invertebrate animals which characterise the Cretaceous age are among

CEPHALOPODA.

_Nautilus sublaevigatus_ and _N. Danicus; Ammonites rostratus; Belemnitella mucronata._

GASTEROPODA.

_Voluta elongata; Phorus ca.n.a.liculatus; Nerinea bisulcata; Pleurotomaria Fleuriausa_, and _P. Santonensis; Natica supracretacea._

ACEPHALA.

_Trigonia scabra; Inoceramus problematicus_ and _I. Lamarckii; Clavigella cretacea; Pholadomya aequivalvis; Spondylus spinosus; Ostrea vesicularis; Ostrea larva; Janira quadricostata; Arca Gravesii; Hippurites Toucasia.n.u.s_ and _H. organisans; Caprina Aguilloni; Radiolites radiosus_, and _R. acuticostus._

BRACHIOPODA.

_Crania Ignabergensis; Terebratula obesa._

POLYZOA (BRYOZOA) AND ESCHINODEMATA.

_Reticulipora obliqua; Ananchytes ovatus; Micraster cor-anguinum, Hemiaster bucardium_ and _H. Fourneli; Galerites albogalerus; Cidaris Forchammeri; Palaeocoma Furstembergii._

1. POLYPI; 2. FORAMINIFERA; 3. AMORPHOZOA.

1. _Cycollites elliptica; Thecosmilia rudis; Enallocnia ramosa; Meandrina Pyrenaica; Synhelia Sharpeana_. 2. _Orbitoides media; Lituola nautiloidea; Flabellina rugosa_. 3. _Coscinopora cupuliformis; Camerospongia fungiformis_.

Among the numerous beings which inhabited the Upper Cretaceous seas there is one which, by its organisation, its proportions, and the despotic empire which it would exercise in the bosom of the waters, is certainly most worthy of our attention. We speak of the _Mosasaurus_, which was long known as the great animal of _Maestricht_, because its remains were found near that city in the most modern of the Cretaceous deposits.

In 1780 a discovery was made in the quarries of Saint Peter's Rocks, near Maestricht, of the head of a great Saurian, which may now be seen in the Museum of Natural History in Paris. This discovery baffled all the science of the naturalists, at a period when the knowledge of these ancient beings was still in its infancy. One saw in it the head of a Crocodile; another, that of a Whale; memoirs and monographs rained down, without throwing much light on the subject. It required all the efforts of Adrian Camper, joined to those of the immortal Cuvier, to a.s.sign its true zoological place to the Maestricht animal. The controversy over this fine fossil engaged the attention of the learned for the remainder of the last century and far into the present.

Maestricht is a city of the Netherlands, built on the banks of the Meuse. At the gates of this city, in the hills which skirt the left or western bank of the river, there rises a solid ma.s.s of cretaceous formation known as Saint Peter's Rocks. In composition these beds correspond with the Meudon chalk beds, and they contain similar fossils.

The quarries are about 100 feet deep, consisting in the upper part of twenty feet abounding in corals and Polyzoa, succeeded by fifty feet of soft yellowish limestone, furnishing a fine building stone, which has been quarried from time immemorial, and extends up to the environs of Liege; this is succeeded by a few inches of greenish soil with Encrinites, and then by a very white chalk with layers of flints. The quarry is filled with marine fossils, often of great size.

These fossil remains, naturally enough, attracted the attention of the curious, and led many to visit the quarries; but of all the discoveries which attracted attention the greatest interest attached to the gigantic animal under consideration. Among those interested by the discovery of these strange vestiges was an officer of the garrison of Maestricht, named Drouin. He purchased the bones of the workmen as the pick disengaged them from the rock, and concluded by forming a collection in Maestricht, which was spoken of with admiration. In 1766, the trustees of the British Museum, hearing of this curiosity, purchased it, and had it removed to London. Incited by the example of Drouin, Hoffmann, the surgeon of the garrison, set about forming a similar collection, and his collection soon exceeded that of Drouin's Museum in riches. It was in 1780 that he purchased of the quarrymen the magnificent fossil head, exceeding six feet in length, which has since so exercised the sagacity of naturalists.

Hoffman did not long enjoy the fruits of his precious prize, however; the chapter of the church of Maestricht claimed, with more or less foundation, certain rights of property; and in spite of all protest, the head of the _Crocodile of Maestricht_, as it was already called, pa.s.sed into the hands of the Dean of the Chapter, named G.o.ddin, who enjoyed the possession of his antediluvian trophy until an unforeseen incident changed the aspect of things. This incident was nothing less than the bombardment and surrender of Maestricht to the Army of the North under Kleber, in 1794.

The Army of the North did not enter upon a campaign to obtain the crania of Crocodiles, but it had on its staff a savant who was devoted to such pacific conquests. Faujas de Saint-Fond, who was the predecessor of Cordier in the Zoological Chair of the Jardin des Plantes, was attached to the Army of the North as Scientific Commissioner; and it is suspected that, in soliciting this mission, our naturalist had in his eye the already famous head of the Crocodile of the Meuse. However that may be, Maestricht fell into the hands of the French, and Faujas eagerly claimed the famous fossil for the French nation, which was packed with the care due to a relic numbering so many thousands of ages, and dispatched to the Museum of Natural History in Paris. On its arrival, Faujas undertook a labour which, as he thought, was to cover him with glory. He commenced the publication of a work ent.i.tled "The Mountain of Saint Peter of Maestricht," describing all the fossil objects found in the Dutch quarry there, especially the _Great Animal_ of Maestricht. He endeavoured to prove that this animal was a Crocodile.

Unfortunately for the glory of Faujas, a Dutch savant had devoted himself to the same study. Adrian Camper was the son of a great anatomist of Leyden, Pierre Camper, who had purchased of the heirs of the surgeon Hoffman some parts of the skeleton of the animal found in the quarry of Saint Peter. He had even published in the _Philosophical Transactions_ of London, as early as 1786, a memoir, in which the animal is cla.s.sed as a Whale. At the death of his father, Adrian Camper re-examined the skeleton, and in a work which Cuvier quotes with admiration, he fixed the ideas which were until then floating about. He proved that the bones belonged neither to a Fish, nor a Whale, nor to a Crocodile, but rather to a particular genus of Saurian Reptiles, or marine lizards, closely resembling in many important structural characters, existing Monitors and Iguanas, and peculiar to rocks of the Cretaceous period, both in Europe and America. Long before Faujas had finished the publication of his work on _La Montagne de Saint-Pierre_ that of Adrian Camper had appeared, and totally changed the ideas of the world on this subject. It did not, however, hinder Faujas from continuing to call his animal the Crocodile of Maestricht. He even announced, some time after, that Adrian Camper was also of his opinion.

"Nevertheless," says Cuvier, "it is as far from the Crocodile as it is from the Iguana; and these two animals differ as much from each other in their teeth, bones, and viscera, as the ape differs from the cat, or the elephant from the horse."

[Ill.u.s.tration: Fig. 145.

_a_, skull of Monitor Niloticus; _b_, under-jaw of same.]

The masterly memoir of Cuvier, while confirming all the views of Camper, has restored the individuality of this surprising being, which has since received the name of Mosasaurus, that is to say, Saurian or Lizard of the Meuse. It appears, from the researches of Camper and Cuvier, that this reptile of the ancient world formed an intermediate genus between the group of the Lacertilia, which comprehends the Monitors (represented in Fig. 145), and the ordinary Lizards; and the Lacertilia, whose palates are armed with teeth, a group which embraces the _Iguana_ and the _Anolis_. In respect to the Crocodiles, the Mosasaurus resembles them in so far as they all belong to the same cla.s.s of Reptiles.

The idea of a lizard, adapted for living and moving with rapidity at the bottom of the water, is not readily conceived; but a careful study of the skeleton of the Mosasaurus reveals to us the secret of this anatomical mechanism. The vertebrae of the animal are concave in front and convex behind; they are attached by means of orbicular or arched articulations, which permitted it to execute easily movements of flexion in any direction. From the middle of the back to the extremity of the tail these vertebrae are deficient in the articular processes which support and strengthen the trunk of terrestrial vertebrated animals: they resemble in this respect the vertebrae of the Dolphins; an organisation necessary to render swimming easy. The tail, compressed laterally at the same time that it was thick in a vertical direction, const.i.tuted a straight rudder, short, solid, and of great power. An arched bone was firmly attached to the body of each caudal vertebra in the same manner as in Fishes, for the purpose of giving increased power to the tail; finally, the extremities of the animal could scarcely be called feet, but rather paddles, like those of the Ichthyosaurus, the Plesiosaurus, and the Whale. We see in Fig. 146 that the jaws are armed with numerous teeth, fixed in their sockets by an osseous base, both large and solid. Moreover, an altogether peculiar dental system occupies the vault of the palate, as in the case of certain Serpents and Fishes, where the teeth are directed backwards, like the barb of a hook, thus opposing themselves to the escape of prey. Such a disposition of the teeth sufficiently proves the destructive character of this Saurian.

[Ill.u.s.tration: Fig. 146.--Head of Mosasaurus Camperi.]

The dimensions of this aquatic lizard, estimated at twenty-four feet, are calculated to excite surprise. But, as we have already seen, the Ichthyosauri and Teleosauri were of great dimensions, as were also the Iguanodon and Megalosaurus, which were ten times the size of living Iguanas. In all these colossal forms we can only see a difference of dimensions, the aggrandis.e.m.e.nt of a type; the laws which affected the organisation of all these beings remain unchanged, they were not errors of Nature--_monstrosities_, as we are sometimes tempted to call them--but simply types, uniform in their structure, and adapted by their dimensions to the physical conditions with which G.o.d had surrounded them.

[Ill.u.s.tration: XXII.--Ideal Landscape of the Cretaceous Period.]

In PLATE XXII. is represented an ideal view of the earth during the _Upper Cretaceous_ period. In the sea swims the Mosasaurus; Molluscs, Zoophytes, and other animals peculiar to the period are seen on the sh.o.r.e. The vegetation seems to approach that of our days; it consists of Ferns and Cycadeae (Pterophyllums), mingled with Palms, Willows, and some dicotyledons of species a.n.a.logous to those of our present epoch. Algae, then very abundant, composed the vegetation of the sea-sh.o.r.e.

We have said that the terrestrial flora of the Upper Cretaceous period was nearly identical with that of the Lower. The marine flora of these two epochs included some Algae, Confervae, and Naadae, among which may be noted the following species: _Confervites fasciculatus_, _Chondrites Mantelli_, _Sarga.s.sites Hynghia.n.u.s_. Among the Naadae, _Zosterites...o...b..gniana_, _Z. lineata_, and several others.

The _Confervae_ are fossils which may be referred, but with some doubt, to the filamentous Algae, which comprehend the great group of the Confervae. These plants were formed of simple or branching filaments, diversely crossing each other; or subdivided, and presenting traces of transverse part.i.tions.