Chapter IX: Part 9

In standard works on natural history the animals under consideration are classed as _mammiferous Didelphæ_. They are brought forth in an imperfect state, and during their transitional condition are suckled in a pouch supported by bones called _marsupial_, which are attached by their extremities to the pelvis, and serve to support the marsupium, whence the animals provided with these provisions for bringing up their progeny are called _Marsupial Mammals_. The Opossum, Kangaroo, and Ornithorhynchus are existing representatives of this group.

The name of _Thylacotherium_, or _Amphitherium_, or _Phascolotherium_, is given to the first of these marsupial Mammals which made their appearance, whose remains have been discovered in the Lower Oolite, and in one of its higher stages, namely, that called the _Great Oolite_. Fig. 110 represents the jaw of the first of these animals, and Fig. 111 the other--both of the natural size. These jaw-bones represent all that has been found belonging to these early marsupial animals; and Baron Cuvier and Professor Owen have both decided as to their origin. The first was found in the Stonesfield quarries. The Phascolotherium, also a Stonesfield fossil, was the ornament of Mr. Broderip’s collection. The animals which lived on the land during the Lower Oolitic period would be nearly the same with those of the Liassic. The insects were, perhaps, more numerous.

The marine fauna included Reptiles, Fishes, Molluscs, and Zoophytes. Among the first were the Pterodactyle, and a great Saurian, the Teleosaurus, belonging to a family which made its appearance in this age, and which reappears in the following epoch. Among the Fishes, the Ganoids and Ophiopsis predominate. Among the Ammonites, _Ammonites Humphriesianus_, _A. Herveyii_ (Fig. 112), _A. Brongniarti_, _Nautilus lineatus_, and many other representatives of the cephalopodous Mollusca. Among the Brachiopods are _Terebratula digona_ (Fig. 113) and _T. spinosa_. Among the Gasteropoda the _Pleurotomaria conoidea_ is remarkable from its elegant shape and markings, and very unlike any of the living _Pleurotoma_ as represented by _P. Babylonia_ (Fig. 114). _Ostrea Marshii_ and _Lima proboscidea_, which belong to the Acephala, are fossil Mollusca of this epoch, to which also belong _Entalophora cellarioides_, _Eschara Ranviliana_, _Bidiastopora cervicornis_; elegant and characteristic molluscous Polyzoa. We give a representation of two living species, as exhibiting the form of these curious beings. (Figs. 115 and 116.)

The Echinoderms and Polyps appear in great numbers in the deposits of the Lower Oolite: _Apiocrinus elegans_, _Hyboclypus gibberulus_, _Dysaster Endesii_ represent the first; _Montlivaltia caryophyllata_, _Anabacia orbulites_, _Cryptocœnia bacciformis_, and _Eunomia radiata_ represent the second.

(Recent Polyzoa.)]

(Recent Polyzoa.)]

This last and most remarkable species of Zoophyte presents itself in great masses many yards in circumference, and necessitates a long period of time for its production. This assemblage of little creatures living under the waters but only at a small depth beneath the surface, as Mr. Darwin has demonstrated, has nevertheless produced banks, or rather islets, of considerable extent, which at one time constituted veritable reefs rising out of the ocean. These reefs were principally constructed in the Jurassic period, and their extreme abundance is one of the characteristics of this geological age. The same phenomenon continues in our day, but by the agency of a new race of zoophytes, which carry on their operations, preparing a new continent, probably, in the _atolls_ of the Pacific Ocean. (See Fig. 108, p. 240.)

1, Otopteris dubia; 2, Otopteris obtusa; 3, Otopteris acuminata; 4, Otopteris cuneata.]

The flora of the epoch was very rich. The Ferns continue to exist, but their size and bearing were sensibly inferior to what they had been in the preceding period. Among them Otopteris, distinguished for its simply pinnated leaves, whose leaflets are auriculate at the base: of the five species, 1, _O. dubia_; and 2, _O. obtusa_; and 3, _O. acuminata_; and 4, _O. cuneata_ (Fig. 117), are from the Oolite. In addition to these we may name _Coniopteris Murrayana_, _Pecopteris Desnoyersii, Pachypteris lanceolata_, and _Phlebopteris Phillipsii_; and among the Lycopods, _Lycopodus falcatus_.

The vegetation of this epoch has a peculiar facies, from the presence of the family of the Pandanaceæ, or screw-pines, so remarkable for their aërial roots, and for the magnificent tuft of leaves which terminates their branches. Neither the leaves nor the roots of these plants have, however, been found in the fossil state, but we possess specimens of their large and spherical fruit, which leave no room for doubt as to the nature of the entire plant.

The Cycads were still represented by the _Zamias_, and by many species of Pterophyllum. The Conifers, that grand family of recent times, to which the pines, firs, and other trees of our northern forests belong, began to occupy an important part in the world’s vegetation from this epoch. The earliest Conifers belonged to the genera _Thuites_, _Taxites_, and _Brachyphyllum_. The _Thuites_ were true _Thuyas_, evergreen trees of the present epoch, with compressed branches, small imbricated and serrated leaves, somewhat resembling those of the Cypress, but distinguished by many points of special organisation. The _Taxites_ have been referred, with some doubts, to the Yews. Finally, the _Brachyphyllum_ were trees which, according to the characteristics of their vegetation, seem to have approached nearly to two existing genera, the _Arthotaxis_ of Tasmania, and the _Weddringtonias_ of South Africa. The leaves of the Brachyphyllum are short and fleshy, with a large and rhomboidal base.

LOWER OOLITE ROCKS.

The formation which represents the Lower Oolite, and which in England attains an average thickness of from 500 to 600 feet, forms a very complex system of stratification, which includes the two formations, _Bajocien_ and _Bathonian_, adopted by M. D’Orbigny and his followers. The lowest beds of the _Inferior Oolite_ occur in Normandy, in the Lower Alps (Basses-Alpes), in the neighbourhoods of Lyons and Neuchatel. They are remarkable near Bayeux for the variety and beauty of their fossils: the rocks are composed principally of limestones--yellowish-brown, or red, charged with hydrated oxide of iron, often oolitic, and reposing on calcareous sands. These deposits are surmounted by alternate layers of clay and marl, blue or yellow--the well-known _Fuller’s Earth_, which is so called from its use in the manufacture of woollen fabrics to extract the grease from the wool. The second series of the Lower Oolite, which attains a thickness of from 150 to 200 feet on the coast of Normandy, and is well developed in the neighbourhood of Caen and in the Jura, has been divided, in Britain, into four formations, in an ascending scale:--

1. The _Great_ or _Bath Oolite_, which consists principally of a very characteristic, fine-grained, white, soft, and well-developed oolitic limestone, at Bath, and also at Caen in Normandy. At the base of the Great Oolite the Stonesfield beds occur, in which were found the bones of the marsupial Mammals, to which we have already alluded; and along with them bones of Reptiles, principally Pterodactyles, together with some finely-preserved fossil plants, fruits, and insects.

2. _Bradford Clay_, which is a bluish marl, containing many fine Encrinites (commonly called stone-lilies), but which had only a local existence, appearing to be almost entirely confined to this formation. “In this case, however,” says Lyell, “it appears that the solid upper surface of the ‘Great Oolite’ had supported, for a time, a thick submarine forest of these beautiful Zoophytes, until the clear and still water was invaded with a current charged with mud, which threw down the stone-lilies, and broke most of their stems short off near the point of attachment. The stumps still remain in their original position.”[65] See Fig. 1, PLATE XIX., p. 261. (Bradford, or Pear, Encrinite.)

[65] “Elements of Geology,” p. 399.

3. _Forest Marble_, which consists of an argillaceous shelly limestone, abounding in marine fossils, and sandy and quartzose marls, is quarried in the forest of Wichwood, in Wiltshire, and in the counties of Dorset, Wilts, and Somerset.

4. The _Cornbrash_ (wheat-lands) consists of beds of rubbly cream-coloured limestone, which forms a soil particularly favourable to the cultivation of cereals; hence its name.[66]

[66] See Bristow in Descriptive Catalogue of Rocks, in _Mus. Pract.
Geol._, p. 134.

_a_, entire figure, reduced; _b_, portion, natural size.

(Recent Coral.)]

The Lower Oolite ranges across the greater part of England, but “attains its maximum development near Cheltenham, where it can be subdivided, at least, into three parts. Passing north, the two lower divisions, each more or less characterised by its own fossils, disappear, and the Ragstone north-east of Cheltenham lies directly upon the Lias; apparently as conformably as if it formed its true and immediate successor, while at Dundry the equivalents of the upper freestones and ragstones (the lower beds being absent) lie directly on the exceedingly thin sands, which there overlie the Lower Lias. In Dorsetshire, on the coast, the series is again perfect, though thin. Near Chipping Norton, in Oxfordshire, the Inferior Oolite disappears altogether, and the Great Oolite, having first overlapped the Fullers’ Earth, passes across the Inferior Oolite, and in its turn seems to lie on the Upper Lias with a regularity as perfect as if no formation in the neighbourhood came between them. In Yorkshire the changed type of the Inferior Oolite, the prevalence of sands, land-plants, and beds of coal, occur in such a manner as to leave no doubt of the presence of terrestrial surfaces on which the plants grew, and all these phenomena lead to the conclusion that various and considerable oscillations of level took place in the British area during the deposition of the strata, both of the Inferior Oolite and of the formations which immediately succeed it.”[67]

[67] President’s Address, by Professor A. C. Ramsay. _Quart. Jour.
Geol. Soc._, 1864, vol. xx., p. 4.

The Inferior Oolite here alluded to is a thin bed of calcareous freestone, resting on, and sometimes replaced by yellow sand, which constitutes the passage-beds from the Liassic series. The Fullers’ Earth clay lies between the limestones of the Inferior and Great Oolite, at the base of which last lies the Stonesfield slate--a slightly oolitic, shelly limestone, or flaggy and fissile sandstone, some six feet thick, rich in organic remains, and ranging through Oxfordshire towards the north-east, into Northamptonshire and Yorkshire. At Colley Weston, in Northamptonshire, fossils of _Pecopteris polypodioides_ are found. In the Great Oolite formation, near Bath, are many corals, among which the _Eunomia radiata_ is very conspicuous. The fossil is not unlike the existing brain-coral of the tropical seas (Fig. 118). The work of this coral seems to have been suddenly stopped by “an invasion,” says Lyell, “of argillaceous matter, which probably put a sudden stop to the growth of Bradford Encrinites, and led to their preservation in marine strata.”[68] The Cornbrash is, in general, a cream-coloured limestone, about forty feet thick, in the south-west of England, and occupying a considerable area in Dorsetshire and North Wilts, as at Cricklade, Malmesbury, and Chippenham, in the latter county. _Terebratula obovata_ is its characteristic shell, and _Nucleolites clunicularis_, _Lima gibbosa_, and _Avicula echinata_ occur constantly in great numbers. Wherever it occurs the Cornbrash affords a rich and fertile soil, well adapted for the growth of wheat, while the Forest Marble, as a soil, is generally poor. The Cornbrash passes downwards into the Forest Marble, and sometimes, as at Bradford, near Bath, is replaced by clay. This clay, called the Bradford clay, is almost wholly confined to the county of Wilts. _Terebratula decussata_ is one of the most characteristic fossils, but the most common is the Apiocrinites or pear-shaped encrinite, whose remains in this clay are so perfectly preserved that the most minute articulations are often found in their natural positions. PLATE XIX., p. 261 (Fig. 1), represents an adult attached by a solid base to the rocky bottom on which it grew, whilst the smaller individuals show the Encrinite in its young state--one with arms expanded, the other with them closed. Ripple-marked slabs of fissile Forest Marble are used as a roofing-slate, and may be traced over a broad band of country in Wiltshire and Gloucestershire, separated from each other by thin seams of clay, in which the undulating ridges of the sand are preserved, and even the footmarks of small Crustaceans are still visible.

[68] “Elements of Geology,” p. 400.

On the opposite page (PLATE XVII.) is represented an ideal landscape of the period of the Lower Oolite. On the shore are types of the vegetation of the period. The _Zamites_, with large trunk covered with fan-like leaves, resembled in form and bearing the existing Zamias of tropical regions; a _Pterophyllum_, with its stem covered from base to summit with its finely-cut feathery leaves; Conifers closely resembling our Cypress, and an arborescent Fern. What distinguishes this sub-period from that of the Lias is a group of magnificent trees, _Pandanus_, remarkable for their aërial roots, their long leaves, and globular fruit.

Upon one of the trees of this group the artist has placed the _Phascolotherium_, not very unlike to our Opossum. It was amongst the first of the Mammalia which appeared in the ancient world. The artist has here enlarged the dimensions of the animal in order to show its form. Let the reader reduce it in imagination one-sixth, for it was not larger than an ordinary-sized cat.

A Crocodile and the fleshless skeleton of the Ichthyosaurus remind us that Reptiles still occupied an important place in the animal creation. A few Insects, especially Dragon-flies, fly about in the air. Ammonites float on the surface of the waves, and the terrible Plesiosaurus, like a gigantic swan, swims about in the sea. The circular reef of coral, the work of ancient Polyps, foreshadows the atolls of the great ocean, for it was during the Jurassic period that the Polyps of the ancient world were most active in the production of coral-reefs and islets.

MIDDLE OOLITE.

The terrestrial flora of this age was composed of Ferns, Cycads, and Conifers. The first represented by the _Pachypteris microphylla_, the second by _Zamites Moreana_. _Brachyphyllum Moreanum_ and _B. majus_ appear to have been the Conifers most characteristic of the period; fruits have also been found in the rocks of the period, which appear to belong to Palms, but this point is still obscure and doubtful.

Numerous vestiges of the fauna which animated the period are also revealed in the rocks of this age. Certain hemipterous insects appear on the earth for the first time, and the Bees among the Hymenoptera, Butterflies among the Lepidoptera, and Dragon-flies among the Neuroptera. In the bosom of the ocean, or upon its banks, roamed the _Ichthyosaurus_, _Ceteosaurus_, _Pterodactylus crassirostris_, and the _Geosaurus_; the latter being very imperfectly known.

The Ceteosaurus whose bones have been discovered in the upper beds of the Great Oolite at Enslow Rocks, at the Kirtlington Railway Station, north of Oxford, and some other places, was a species of Crocodile nearly resembling the modern Gavial or Crocodile of the Ganges. This huge whale-like reptile has been described by Professor John Phillips as unmatched in size and strength by any of the largest inhabitants of the Mesozoic land or sea--perhaps the largest animal that ever walked upon the earth. A full-grown Ceteosaurus must have been _at least_ fifty feet long, ten feet high, and of a proportionate bulk. In its habits it was, probably, a marsh-loving or river-side animal, dwelling amidst filicene, cycadaceous, and coniferous shrubs and trees full of insects and small mammalia. The one small and imperfect tooth which has been found resembles that of Iguanodon more than of any other reptile; and it seems probable that the Ceteosaurus was nourished by vegetable food, which abounded in the vicinity of its haunts, and was not obliged to contend with the Megalosaurus for a scanty supply of more stimulating diet.[69]

[69] For a full account of the Ceteosaurus, see “The Geology of the
Thames Valley,” by Prof. John Phillips, F.R.S. 1871.

Another reptile allied to the Pterodactyle lived in this epoch--the _Ramphorynchus_, distinguished from the Pterodactyle by a long tail. The imprints which this curious animal has left upon the sandstone of the period are impressions of its feet and the linear furrow made by its tail. Like the Pterodactyle, the Ramphorynchus, which was about the size of a crow, could not precisely fly, but, aided by the wing (a sort of natural parachute formed by the membrane connecting the fingers with the body), it could throw itself from a height upon its prey. Fig. 119 represents a restoration of this animal. The footprints in the soil are in imitation of those which accompany the remains of the Ramphorynchus in the Oolitic rocks, and they show the imprints of the anterior and posterior feet and also the marks made by the tail.

This tail was very long, far surpassing in length the rest of the vertebral column, and consisting of more than thirty vertebræ--which were at first short, but rapidly elongate, retain their length for a considerable distance, and then gradually diminish in size.

Another genus of Reptiles appears in the Middle Oolite, of which we have had a glimpse in the Lias and Great Oolite of the preceding section. This is the _Teleosaurus_, which the recent investigations of M. E. Deslongchamps allow of re-construction. The Teleosaurus enables us to form a pretty exact idea of these Crocodiles of the ancient seas--these cuirassed Reptiles, which the German geologist Cotta describes as “the great barons of the kingdom of Neptune, armed to the teeth, and clothed in an impenetrable panoply; the true filibusters of the primitive seas.”

The Teleosaurus resembled the Gavials of India. The former inhabited the banks of rivers, perhaps the sea itself; they were longer, more slender, and more active than the living species; they were about thirty feet in length, of which the head may be from three to four feet, with their enormous jaws sometimes with an opening of six feet, through which they could engulf, in the depths of their enormous throat, animals of considerable size.

The _Teleosaurus cadomensis_ is represented on the opposite page (PLATE XVIII.), after the sketch of M. E. Deslongchamps, carrying from the sea in its mouth a _Geoteuthis_, a species of Calamary of the Oolitic epoch. This creature was coated with a cuirass both on the back and belly. In order to show this peculiarity, a living individual is represented on the shore, and a dead one is floating on its back in shallow water, leaving the ventral cuirass exposed.

Behind the _Teleosaurus cadomensis_ in the engraving, another Saurian, the _Hylæosaurus_, is represented, which makes its appearance in the Cretaceous epoch. We have here adopted the restoration which has been so ably executed by Mr. Waterhouse Hawkins, at the Crystal Palace, Sydenham.

Besides the numerous Fishes with which the Oolitic seas swarmed, they contained some Crustaceans, Cirripedes, and various genera of Mollusca and Zoophytes. _Eryon arctiformis_, represented in Fig. 119, belongs to the class of Crustaceans, of which the spiny lobster is the type. Among the Mollusca were some Ammonites, Belemnites, and Oysters, of which many hundred species have been described. Of these we may mention _Ammonites refractus, A. Jason and A. cordatus, Ostrea dilatata, Terebratula diphya, Diceras arietena, Belemnites hastatus_, and _B. Puzosianus_. In some of the finely-laminated clays the Ammonites are very perfect, but somewhat compressed, with the outer lip or margin of the aperture entire (Fig. 120). Similar prolongations have been noticed in Belemnites found by Dr. Mantell in the Oxford Clay, near Chippenham.

Among the Echinoderms, _Cidaris glandiferus_, _Apiocrinus Roissyanus_, and _A. rotundus_, the graceful _Saccocoma pectinata_, _Millericrinus nodotianus_, _Comatula costata_, and _Hemicidaris crenularis_ may be mentioned; _Apiocrinites rotundus_, figured in PLATE XIX., is a reduced restoration: 1, being expanded; _a_, closed; 3, a cross section of the upper extremity of the pear-shaped head; 4, a vertical section showing the enlargement of the alimentary canal, with the hollow lenticular spaces which descend through the axis of the column, forming the joints, and giving elasticity and flexure to the whole stem, without risk of dislocation. _A. rotundus_ is found at Bradford in Wiltshire, Abbotsbury in Dorset, at Soissons, and Rochelle. This species--known as the Bradford Pear-Encrinite--is only found in the strata mentioned.

The Corals of this epoch occur in great abundance. We have already remarked that these aggregations of Polyps are often met with at a great depth in the strata. These small calcareous structures have been formed in the ancient seas, and the same phenomenon is extending the terrestrial surface in our days in the seas of Oceania, where reefs and atolls of coral are rising by slow and imperceptible steps, but with no less certainty. Although their mode of production must always remain to some extent a mystery, the investigations of M. Lamaroux, Mr. Charles Darwin, and M. D’Orbigny have gone a long way towards explaining their operations; for the Zoophyte in action is an aggregation of these minute Polyps. Describing what he believes to be a sea-pen, a Zoophyte allied to _Virgularia Patagonia_, Mr. Darwin says: “It consists of a thin, straight, fleshy stem, with alternate rows of polypi on each side, and surrounding an elastic stony axis. The stem at one extremity is truncate, but at the other is terminated by a vermiform fleshy appendage. The stony axis which gives strength to the stem, may be traced at this extremity into a mere vessel filled with granular matter. At low water hundreds of these zoophytes might be seen, projecting like stubble, with the truncate end upwards, a few inches above the surface of the muddy sand. When touched or pulled, they drew themselves in suddenly, with force, so as nearly or quite to disappear. By this action, the highly-elastic axis must be bent at the lower extremity, where it is naturally slightly curved; and I imagine it is by this elasticity alone that the zoophyte is enabled to rise again through the mud. Each polypus, though closely united to its brethren, has a distinct mouth, body, and tentacula. Of these polypi, in a large specimen there must be many thousands. Yet we see that they act by one movement; that they have one central axis, connected with a system of obscure circulation.” Such is the brief account given by a very acute observer of these singular beings. They secrete the calcareous matter held in solution in the oceanic waters, and produce the wonderful structures we have now under consideration; and these calcareous banks have been in course of formation during many geological ages. They just reach the level of the waters, for the polyps perish as soon as they are so far above the surface that neither the waves nor the flow of the tides can reach them. In the Oolitic rocks these banks are frequently found from twelve to fifteen feet thick, and many leagues in length, and preserving, for the most part, the relative positions which they occupied in the sea while in course of formation.

The rocks which now represent the Middle Oolitic Period are usually divided into the _Oxford Clay_, the lower member of which is an arenaceous limestone, known as the _Kellaways Rock_, which in Wiltshire and other parts of the south-west of England attains a thickness of eight or ten feet, with the impressions of numerous Ammonites, and other shells. In Yorkshire, around Scarborough, it reaches the thickness of thirty feet; and forms well-developed beds of bluish-black marl in the department of Calvados, in France. It is the base of this clay which forms the soil (_Argile de Dives_) of the valley of the Auge, renowned for its rich pasturages and magnificent cattle. The same beds form the base of the oddly-shaped but fine rocks of La Manche, which are popularly known as the _Vaches Noires_ (or black cows)--a locality celebrated, also, for its fine Ammonites transformed into pyrites.

The _Oxford Clay_ constitutes the base of the hills in the neighbourhood of Oxford, forming a bed of clay sometimes more than 600 feet thick. It is found well-developed in France, at Trouville, in the department of the Calvados; and at Neuvisy, in the department of the Ardennes, where it attains a thickness of about 300 feet. It is a bluish, sometimes whitish limestone (often argillaceous), and bluish marl. The _Gryphæa dilatata_ is the most common fossil in the Oxford Clay. The _Coral Rag_ is so called from the fact that the limestone of which it is chiefly composed consists, in part, of an aggregation of considerable masses of petrified Corals; not unlike those now existing in the Pacific Ocean, supposing them to be covered up for ages and fossilised. This coral stratum extends through the hills of Berkshire and North Wilts, and it occurs again near Scarborough. In the counties of Dorset, Bedford, Buckingham, and Cambridge, and some other parts of England, the limestone of the Coral Rag disappears and is replaced by clay--in which case the Oxford Clay is overlaid directly by the Kimeridge Clay. In France it is found in the departments of the Meuse, of the Yonne, of the Ain, of the Charente Inférieure. In the Alps the _Diceras limestone_ is regarded, by most geologists, as coeval with the English Coral Rag.

UPPER OOLITE.

Some marsupial Mammals have left their remains in the Upper Oolite as in the Lower. They belong to the genus _Sphalacotherium_. Besides the Plesiosauri and Teleosauri, there still lived in the maritime regions a Crocodile, the _Macrorhynchus_; and the monstrous _Pœcilopleuron_, with sharp cutting teeth, one of the most formidable animals of this epoch; the _Hylæosaurus_, _Cetiosaurus_, _Stenosaurus_, and _Streptospondylus_, and among the Turtles, the _Emys_ and _Platemys_. As in the Lower Oolite, so also in the Upper, Insects similar to those by which we are surrounded, pursued their flight in the meadows and hovered over the surface of the water. Of these, however, too little is known for us to give any very precise indication on the subject of their special organisation.

The most remarkable fact relating to this period is the appearance of the first bird. Hitherto the Mammals, and of these only imperfectly-organised species, namely, the Marsupials, have alone appeared. It is interesting to witness birds appearing immediately after. In the quarries of lithographic stone at Solenhofen, the remains of a bird, with feet and feathers, have been found, but without the head. These curious remains are represented in Fig. 122, in the position in which they were discovered. The bird is usually designated the Bird of Solenhofen.

Shell of Physa fontinalis.]

The Oolitic seas of this series contained Fishes belonging to the genera _Asteracanthus_, _Strephodes_, _Lepidotus_, and _Microdon_. The Cephalopodous Mollusca were not numerous, the predominating genera belonging to the Lamellibranchs and to the Gasteropods, which lived on the shore. The reef-making Madrepores or Corals were more numerous. A few Zoophytes in the fossil state testify to the existence of these extraordinary animals. The fossils characteristic of the fauna of the period include _Ammonites decipiens_ and _A. giganteus_, _Natica elegans_ and _hemispherica_, _Ostrea deltoidea_ and _O. virgula_, _Trigonia gibbosa_, _Pholadomya multicostata_ and _P. acuticostata_, _Terebratula subsella_, and _Hemicidaris Purbeckensis_. Some _Fishes_, _Turtles_, _Paludina_, _Physa_ (Fig. 123), _Unio_, _Planorbis_ (Fig. 201), and the little crustacean bivalves, the Cypris, constituted the fresh-water fauna of the period.

The terrestrial flora of the period consisted of Ferns, Cycadeaceæ, and Conifers; in the ponds and swamps some Zosteræ. The _Zosteræ_ are monocotyledonous plants of the family of the Naïdaceæ, which grow in the sandy mud of maritime regions, forming there, with their long, narrow, and ribbon-like leaves, vast prairies of the most beautiful green. At low tides these masses of verdure appear somewhat exposed. They would form a retreat for a great number of marine animals, and afford nourishment to others.

* * * * *

On the opposite page an ideal landscape of the period (PLATE XX.) represents some of the features of the Upper Oolite, especially the vegetation of the Jurassic period. The _Sphenophyllum_, among the Tree-ferns, is predominant in this vegetation; some _Pandanas_, a few _Zamites_, and many _Conifers_, but we perceive no Palms. A coral islet rises out of the sea, having somewhat of the form of the _atolls_ of Oceania, indicating the importance these formations assumed in the Jurassic period. The animals represented are the _Crocodileimus_ of Jourdan, the _Ramphorynchus_, with the imprints which characterise its footsteps, and some of the invertebrated animals of the period, as the _Asteria_, _Comatula_, _Hemicidaris_, _Pteroceras_. Aloft in the air floats the bird of Solenhofen, the _Archæopteryx_, which has been re-constructed from the skeleton, with the exception of the head, which remains undiscovered.

* * * * *

The rocks which represent the Upper Oolite are usually divided into two series: 1. The _Purbeck Beds_; 2. The _Portland Stone and Sand_; and 3. The _Kimeridge Clay_.

The _Kimeridge Clay_, which in many respects bears a remarkable resemblance to the Oxford Clay, is composed of blue or yellowish argillaceous beds, which occur in the state of clay and shale (containing locally beds of bituminous schist, sometimes forming a sort of earthy impure coal), and several hundred feet in thickness. These beds are well developed at Kimeridge, in Dorsetshire, whence the clay takes its name. In some parts of Wiltshire the beds of bituminous matter have a shaly appearance, but there is an absence of the impressions of plants which usually accompany the bitumen, derived from the decomposition of plants. These rocks, with their characteristic fossils, _Cardium striatulum_ and _Ostrea deltoidea_, are found throughout England: in France, at Tonnerre, Dept. Yonne; at Havre; at Honfleur; at Mauvage; in the department of the Meuse it is so rich in shells of _Ostrea deltoidea_ and _O. virgula_, that, “near Clermont in Argonne, a few leagues from St. Menehould,” says Lyell,[70] “where these indurated marls crop out from beneath the Gault, I have seen them (_Gryphæa virgula_) on decomposing leave the surface of every ploughed field literally strewed over with this fossil oyster.”

[70] “Elements of Geology,” p. 393.

The second section of this series consists of the oolitic limestone of Portland, which is quarried in the Isle of Portland and in the cliffs of the Isle of Purbeck in Dorsetshire, and also at Chilmark in the Vale of Wardour, in Wiltshire. In France, the Portland beds are found near Boulogne, at Cirey-le-Château, Auxerre, and Gray (Haute Saône).

The Isle, or rather peninsula of Portland,[71] off the Dorsetshire coast, rises considerably above the sea-level, presenting on the side of the port a bold line of cliffs, connected with the mainland by the Chesil bank,[72] an extraordinary formation, consisting of a beach of shingle and pebbles loosely piled on the blue Kimeridge clay, and stretching ten miles westward along the coast. The quarries are chiefly situated in the northerly part of the island. The story told of this remarkable island is an epitome of the revolutions the surface of the earth has undergone. The slaty Purbeck beds which overlie the Portland stone are of a dark-yellowish colour; they are burnt in the neighbourhood for lime. The next bed is of a whiter and more lively colour. It is the stone of which the portico of St. Paul’s and many of the houses of London, built in Queen Anne’s time, were constructed. The building-stone contains fossils exclusively marine. Upon this stratum rests a bed of limestone formed in lacustrine waters. Finally, upon this bed rests another deposit of a substance which consists of very well-preserved vegetable earth or _humus_, quite analogous to our vegetable soil, of the thickness of from fifteen to eighteen inches, and of a blackish colour; it contains a strong proportion of carbonaceous earth; it abounds in the silicified remains of Conifers and other plants, analogous to the _Zamia_ and _Cycas_--this soil is known as the “dirt-bed.” The trunks of great numbers of silicified trees and tropical plants are found here erect, their roots fixed in the soil, and of species differing from any of our forest trees. “The ruins of a forest upon the ruins of a sea,” says Esquiros, “the trunks of these trees were petrified while still growing. The region now occupied by the narrow channel and its environs had been at first a sea, in whose bed the Oolitic deposits which now form the Portland stone accumulated: the bed of the sea gradually rose and emerged from the waves. Upon the land thus rescued from the deep, plants began to grow; they now constitute with their ruins the soil of the dirt-bed. This soil, with its forest of trees, was afterwards plunged again into the waters--not the bitter waters of the ocean, but in the fresh waters of a lake formed at the mouth of some great river.”

[71] For details respecting these strata the reader may consult, with
advantage, the useful handbook to the geology of Weymouth and
Portland, by Robert Damon.

[72] See Bristow and Whitaker “On the Chesil Bank,” _Geol. Mag._, vol.
vi., p. 433.

Time passed on, however; a calcareous sediment brought from the interior by the waters, formed a layer of mud over the dirt-bed; finally, the whole region was covered by a succession of calcareous deposits, until the day when the Isle of Portland was again revealed to light. “From the facts observed,” says Lyell, “we may infer:--1. That those beds of the Upper Oolite, called the Portland, which are full of marine shells, were overspread with fluviatile mud, which became dry land, and covered with a forest, throughout a portion of space now occupied by the south of England, the climate being such as to admit of the growth of the _Zamia_ and _Cycas_. 2. This land at length sank down and was submerged with its forest beneath a body of fresh water from which sediment was thrown down enveloping fluviatile shells. 3. The regular and uniform preservation of this thin bed of black earth over a distance of many miles, shows that the change from dry land to the state of a fresh-water lake, or estuary, was not accompanied by any violent denudation or rush of water, since the loose black earth, together with the trees which lay prostrate on its surface, must inevitably have been swept away had any such violent catastrophe taken place.”[73]

[73] “Elements of Geology,” p. 389.

The soil known as the _dirt-bed_ is nearly horizontal in the Isle of Portland; but we discover it again not far from there in the sea-cliffs of the Isle of Purbeck, having an inclination of 45°, where the trunks continue perfectly parallel among themselves, affording a fine example of a change in the position of beds originally horizontal. Fig. 124 represents this species of geological _humus_. “Each _dirt-bed_” says Sir Charles Lyell, “may, no doubt, be the memorial of many thousand years or centuries, because we find that two or three feet of vegetable soil is the only monument which many a tropical forest has left of its existence ever since the ground on which it now stands was first covered with its shade.”[74]

[74] Ibid, p. 391.

This bed of vegetable soil is, then, near the summit of that long and complicated series of beds which constitute the Jurassic period; these ruins, still vegetable, remind us forcibly of the coal-beds, for they are nothing else than a less advanced state of that kind of vegetable fossilisation which was perfected on such an immense scale, and during an infinite length of time in the coal period.

The Purbeck beds, which are sometimes subdivided into Lower, Middle, and Upper, are mostly fresh-water formations, intimately connected with the Upper Portland beds. But there they begin and end, being scarcely recognisable except in Dorsetshire, in the sea-cliffs of which they were first studied. They are finely exposed in Durdlestone Bay, near Swanage, and at Lulworth Cove, on the same coast. The _lower beds_ consist of a purely fresh-water marl, eighty feet thick, containing shells of _Cypris_, _Limnæa_, and some _Serpulæ_ in a bed of marl of brackish-water origin, and some _Cypris_-bearing shales, strangely broken up at the west end of the Isle of Purbeck.

The _Middle series_ consists of twelve feet of marine strata known as the “cinder-beds,” formed of a vast accumulation of _Ostrea distorta_, resting on fresh-water strata full of _Cypris fasciculata_, _Planorbis_, and _Limnæa_, by which this strata has been identified as far inland as the vale of Wardour in Wiltshire. Above the cinder-beds are shales and limestones, partly of fresh-water and partly of brackish-water origin, in which are Fishes, many species of Lepidotus, and the crocodilian reptile, _Macrorhynchus_. On this rests a purely marine deposit, with _Pecten_, _Avicula_, &c. Above, again, are brackish beds with _Cyrena_, overlying which is thirty feet of fresh-water limestone, with _Fishes_, _Turtles_, and _Cyprides_.

The _upper beds_ are purely fresh-water strata, about fifty feet thick, containing _Paludina_, _Physa_, _Limnæa_, all very abundant. In these beds the Purbeck marble, formerly much used in the ornamental architecture of the old English cathedrals, was formerly quarried. (See Note, page 274.)

* * * * *

A few words may be added, in explanation of the term _oolite_, applied to this sub-period of the Jurassic formation. In a great number of rocks of this series the elements are neither crystalline nor amorphous--they are, as we have already said, oolitic; that is to say, the mass has the form of the roe of certain fishes. The question naturally enough arises, Whence this singular oolitic structure assumed by the components of certain rocks? It is asserted that the grinding action of the sea acting upon the precipitated limestone produces rounded forms analogous to grains of sand. This hypothesis may be well founded in some cases. The marine sediments which are deposited in some of the warm bays of Teneriffe are found to take the spheroidal granulated form of the oolite. But these local facts cannot be made to apply to the whole extent of the oolitic formations. We must, therefore, look further for an explanation of the phenomena.

It is admitted that if the cascades of Tivoli, for example, can give birth to the oolitic grains, the same thing happens in the quietest basins, that in stalactite-caverns oolitic grains develop themselves, which afterwards, becoming cemented together from the continued, but very slow, affluence of the calcareous waters, give rise to certain kinds of oolitic rocks.

On the other hand, it is known that nodules, more or less large, develop themselves in marls in consequence of the concentration of the calcareous elements, without the possibility of any wearing action of water. Now, as there exists every gradation of size between the smallest oolitic grains and the largest concretions, it is reasonable to suppose that the oolites are equally the product of concentration.

Finally, from research to research, it is found that perfectly constituted oolites--that is to say, concentric layers, as in the Jurassic limestone--develop themselves in vegetable earth in places where the effects of water in motion is not more admissible than in the preceding instances.

Thus we arrive at the conclusion, that if Nature sometimes forms crystals with perfect terminations in magmas in the course of solidification, she gives rise also to spheroidal forms surrounding various centres, which sometimes originate spontaneously, and in other cases are accumulated round the débris of fossils, or even mere grains of sand. Nevertheless, all mineral substances are not alike calculated to produce oolitic rocks; putting aside some particular cases, this property is confined to limestone and oxide of iron.

* * * * *

With regard to the distribution of the Jurassic formation on the terrestrial globe, it may be stated that the Cotteswold Hills in England, and in France the Jura mountains, are almost entirely composed of these rocks, the several series of beds being all represented in them--this circumstance, in fact, induced Von Humboldt to name the formation after this latter range. The Upper Lias also exists in the Pyrenees and in the Alps; in Spain; in many parts of Northern Italy; in Russia, especially in the government of Moscow, and in the Crimea; but it is in Germany where it occupies the most important place. A thin bed of oolitic limestone presents, at Solenhofen in Bavaria, a geological repository of great celebrity, containing fossil Plants, Fishes, Insects, Crustaceans, with some Pterodactyles, admirably preserved; it yielded also some of the earliest of the feathered race. The fine quarries of lithographic stone at Pappenheim, so celebrated all over Europe, belong to the Jurassic formation.

It has recently been announced that these rocks have been found in India; they contribute largely to the formation of the main mass of the Himalayas, and to the chain of the Andes in South America; finally, from recent investigations, they seem to be present in New Zealand.

In England the Lias constitutes a well-defined belt about thirty miles broad, extending from Dorsetshire, in the south, to Yorkshire, in the north, formed of alternate beds of clay, shales, and limestone (with layers of jet), on the coast near Whitby. It is rich, as we have seen, in ancient life, and that in the strongest forms imaginable. From the unequal hardness of the rocks it comprises, it stands out boldly in some of the minor ranges of hills, adding greatly to the picturesque beauty of the scenery in the centre of the country. In Scotland the formation occupies a very limited space.

A map of the country at the close of the Jurassic period would probably show double the extent of dry land in the British Islands, compared with what it displayed as an island in the primordial ocean; but Devon and Cornwall had long risen from the sea, and it is probable that the Jurassic beds of Dorsetshire and France were connected by a tongue of land running from Cherbourg to the Liassic beds of Dorsetshire, and that Boulogne, still an island, was similarly connected with the Weald.

NOTE.--Sections of the Purbeck strata of Dorsetshire have been
constructed by Mr. Bristow, from actual measurement, in the
several localities in the Isle of Purbeck, where they are most
clearly and instructively displayed.

These sections, published by the Geological Survey, show in
detail the beds in their regular and natural order of
succession, with the thickness, mineral character, and contents,
as well as the fossils, of each separate bed.

THE CRETACEOUS PERIOD.

The name _Cretaceous_ (from _creta_, chalk) is given to this epoch in the history of our globe because the rocks deposited by the sea, towards its close, are almost entirely composed of chalk (carbonate of lime).

Carbonate of lime, however, does not now appear for the first time as a part of the earth’s crust; we have already seen limestone occurring, among the terrestrial materials, from the Silurian period; the Jurassic formation is largely composed of carbonate of lime in many of its beds, which are enormous in number as well as extent; it appears, therefore, that in the period called _Cretaceous_ by geologists, carbonate of lime was no new substance in the constitution of the globe. If geologists have been led to give this name to the period, it is because it accords better than any other with the characteristics of the period; with the vast accumulations of chalky or earthy limestone in the Paris basin, and the beds of so-called Greensand, and Chalk of the same age, so largely developed in England.

We have already endeavoured to establish the origin of lime, in speaking of the Silurian and Devonian periods, but it may be useful to recapitulate the explanation here, even at the risk of repeating ourselves.

We have said that lime was, in all probability, introduced to the globe by thermal waters flowing abundantly through the fissures, dislocations, and fractures in the ground, which were themselves caused by the gradual cooling of the globe; the central nucleus being the grand reservoir and source of the materials which form the solid crust. In the same manner, therefore, as the several eruptive substances--such as granites, porphyries, trachytes, basalts, and lava--have been ejected, so have thermal waters charged with carbonate of lime, and often accompanied by silica, found their way to the surface in great abundance, through the fissures, fractures, and dislocations in the crust of the earth. We need only mention here the Iceland geysers, the springs of Plombières, and the well-known thermal springs of Bath and elsewhere in this country.

But how comes lime in a state of bicarbonate, dissolved in these thermal waters, to form rocks? That is what we propose to explain.

During the primary geological periods, thermal waters, as they reached the surface, were discharged into the sea and united themselves with the waves of the vast primordial ocean, and the waters of the sea became sensibly calcareous--they contained, it is believed, from one to two per cent. of lime. The innumerable animals, especially Zoophytes, and Mollusca with solid shells, with which the ancient seas swarmed, secreted this lime, out of which they built up their mineral dwelling--or shell. In this liquid and chemically calcareous medium, the Foraminifera and Polyps of all forms swarmed, forming an innumerable population. Now what became of the bodies of these creatures after death? They were of all sizes, but chiefly microscopic; that is, so small as to be individually all but invisible to the naked eye. The perishable animal matter disappeared in the bosom of the waters by decomposition, but there still remained behind the indestructible inorganic matter, that is to say, the carbonate of lime forming their testaceous covering; these calcareous deposits accumulating in thick beds at the bottom of the sea, became compacted into a solid mass, and formed a series of continuous beds superimposed on each other. These, increasing imperceptibly in the course of ages, ultimately formed the rocks of the _Cretaceous_ period, which we have now under consideration.

These statements are not, as the reader might conceive from their nature, a romantic conception invented to please the imagination of those in search of a system--the time is past when geology should be regarded as the romance of Nature--nor has what we advance at all the character of an arbitrary conception. One is no doubt struck with surprise on learning, for the first time, that all the limestone rocks, all the calcareous stones employed in the construction of our dwellings, our cities, our castles and cathedrals, were deposited in the seas of an earlier world, and are only composed of an aggregation of shells of Mollusca, or fragments of the testaceous coverings of Foraminifera and other Zoophytes--nay, that they were secreted from the water itself, and then assimilated by these minute creatures, and that this would appear to have been the great object of their creation in such myriads. Whoever will take the trouble to observe, and reflect on what he observes, will find all his doubts vanish. If chalk be examined with a microscope, it will be found to be composed of the remains of numerous Zoophytes, of minute and divers kinds of shells, and, above all, of Foraminifera, so small that their very minuteness seems to have rendered them indestructible. A hundred and fifty of these small beings placed end to end, in a line, will only occupy the space of about one-twelfth part of an inch.

Fig. 126.--Chalk of Meudon (magnified).]

Much of this curious information was unknown, or at least only suspected, when Ehrenberg began his microscopical investigations. From small samples of chalk reduced to powder, placed upon the object-glass, and examined under the microscope, Ehrenberg prepared the designs which we reproduce from his learned micrographical work, in which some of the elegant forms discovered in the Chalk are illustrated, greatly magnified. Fig. 126 represents the chalk of Meudon, in France, in which ammonite-like forms of Foraminifera and others, equally beautiful, appear. Fig. 127, from the chalk of Gravesend, contains similar objects. Fig. 128 is an example of chalk from the island of Moën, in Denmark; and Fig. 129, that which is found in the Tertiary rocks of Cattolica, in Sicily. In all these the shells of Ammonites appear, with clusters of round Foraminifera and other Zoophytes. In two of these engravings (Figs. 126 and 128), the chalk is represented in two modes--in the upper half, by transparency or transmitted light; in the lower half, the mass is exhibited by superficial or reflected light.

Fig. 127.--Chalk of Gravesend. (After Ehrenberg).--Magnified.]

Observation, then, establishes the truth of the explanation we have given concerning the formation of the chalky or Cretaceous rocks; but the question still remains--How did these rocks, originally deposited in the sea, become elevated into hills of great height, with bold escarpments, like those known in England as the North and South Downs? The answer to this involves the consideration of other questions which have, at present, scarcely got beyond hypothesis.

Fig. 128.--Chalk of the Isle of Moën, Denmark.]

Fig. 129.--Chalk of Cattolica, Sicily (magnified).]

During and after the deposition of the Portland and Purbeck beds, the entire Oolite Series, in the south and centre of England and other regions, was raised above the sea-level and became dry land. Above these Purbeck beds, as Professor Ramsay tells us [in the district known as the Weald], “we have a series of beds of clays, sandstones, and shelly limestones, indicating by their fossils that they were deposited in an estuary where fresh water and occasionally brackish water and marine conditions prevailed. The Wealden and Purbeck beds indeed represent the delta of an immense river which in size may have rivalled the Ganges, Mississippi, Amazon, &c., and whose waters carried down to its mouth the remains of land-plants, small Mammals, and great terrestrial Reptiles, and mingled them with the remains of Fishes, Molluscs, and other forms native to its waters. I do not say that this immense river was formed or supplied by the drainage of what we now call Great Britain--I do not indeed know where this continent lay, but I do know that England formed a part of it, and that in size it must have been larger than Europe, and was probably as large as Asia, or the great continent of America.” Speaking of the geographical extent of the Wealden, Sir Charles Lyell says: “It cannot be accurately laid down, because so much of it is concealed beneath the newer marine formations. It has been traced about 200 miles from west to east; from the coast of Dorsetshire to near Boulogne, in France; and nearly 200 miles from north-west to south-east, from Surrey and Hampshire to Beauvais, in France;”[75] but he expresses doubt, supposing the formation to have been continuous, if the two areas were contemporaneous, the region having undergone frequent changes, the great estuary having altered its form, and even shifted its place. Speaking of a hypothetical continent, Sir Charles Lyell says: “If it be asked where the continent was placed from the ruins of which the Wealden strata were derived, and by the drainage of which a great river was fed, we are half tempted to speculate on the former existence of the Atlantis of Plato. The story of the submergence of an ancient continent, however fabulous in history, must have been true again and again as a geological event.”[76]

[75] “Elements of Geology,” p. 349.

[76] Ibid, p. 350.

The proof that the Wealden series were accumulated under fresh-water conditions and as a river deposit[77] lies partly in the nature of the strata, but chiefly in the nature of the organic remains. The fish give no positive proof, but a number of Crocodilian reptiles give more conclusive evidence, together with the shells, most of them being of fresh-water origin, such as Paludina, Planorbis, Lymnæa, Physa, and such like, which are found living in many ponds and rivers of the present day. Now and then we find bands of marine remains, not mixed with fresh-water deposits, but interstratified with them; showing that at times the mouth and delta of the river had sunk a little, and that it had been invaded by the sea; then by gradual change it was lifted up, and became an extensive fresh-water area. This episode at last comes to an end by the complete submergence of the Wealden area; and upon these fresh-water strata a set of marine sands and clays, and upon these again thick beds of pure white earthy limestone of the Cretaceous period were deposited. The lowest of these formations is known as the Lower Greensand; then followed the clays of the Gault, which were succeeded by the Upper Greensand. Then, resting upon the Upper Greensand, comes the vast mass of Chalk which in England consists of soft white earthy limestone, containing, in the upper part, numerous bands of interstratified flints, which were mostly sponges originally, that have since become silicified and converted into flint. The strata of chalk where thickest are from 1,000 to 1,200 feet in thickness. Their upheaval into dry land brought this epoch to an end; the conditions which had contributed to its formation ceased in our area, and as the uppermost member of the Secondary rocks, it closes the record of Mesozoic times in England.

[77] “The Physical Geology and Geography of Great Britain,” by A. C.
Ramsay, F.R.S., p. 64.