The World Before the Deluge Part 20

Darwin has demonstrated, has nevertheless produced banks, or rather islets, of considerable extent, which at one time const.i.tuted veritable reefs rising out of the ocean. These reefs were princ.i.p.ally constructed in the Jura.s.sic 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.)

[Ill.u.s.tration: Fig. 117.

1, Otopteris dubia; 2, Otopteris obtusa; 3, Otopteris ac.u.minata; 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.

ac.u.minata_; 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 Pandanaceae, or screw-pines, so remarkable for their aerial 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 (Ba.s.ses-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 princ.i.p.ally 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 princ.i.p.ally 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, princ.i.p.ally 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 sh.e.l.ly limestone, abounding in marine fossils, and sandy and quartzose marls, is quarried in the forest of Wichwood, in Wilts.h.i.+re, 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.

[Ill.u.s.tration: Fig. 118.--Meandrina Daedalaea.

_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. Pa.s.sing 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 Dorsets.h.i.+re, on the coast, the series is again perfect, though thin. Near Chipping Norton, in Oxfords.h.i.+re, the Inferior Oolite disappears altogether, and the Great Oolite, having first overlapped the Fullers' Earth, pa.s.ses 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 Yorks.h.i.+re 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 const.i.tutes the pa.s.sage-beds from the Lia.s.sic 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, sh.e.l.ly limestone, or flaggy and fissile sandstone, some six feet thick, rich in organic remains, and ranging through Oxfords.h.i.+re towards the north-east, into Northamptons.h.i.+re and Yorks.h.i.+re. At Colley Weston, in Northamptons.h.i.+re, 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 Dorsets.h.i.+re and North Wilts, as at Cricklade, Malmesbury, and Chippenham, in the latter county. _Terebratula obovata_ is its characteristic sh.e.l.l, 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 pa.s.ses 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 Wilts.h.i.+re and Gloucesters.h.i.+re, 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.

[Ill.u.s.tration: XVII.--Ideal Landscape of the Lower Oolite Period.]

On the opposite page (PLATE XVII.) is represented an ideal landscape of the period of the Lower Oolite. On the sh.o.r.e 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, _Panda.n.u.s_, remarkable for their aerial 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 Jura.s.sic 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, b.u.t.terflies among the Lepidoptera, and Dragon-flies among the Neuroptera. In the bosom of the ocean, or upon its banks, roamed the _Ichthyosaurus_, _Ceteosaurus_, _Pterodactylus cra.s.sirostris_, 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 surpa.s.sing in length the rest of the vertebral column, and consisting of more than thirty vertebrae--which were at first short, but rapidly elongate, retain their length for a considerable distance, and then gradually diminish in size.

[Ill.u.s.tration: XVIII.--Ideal landscape of the Middle Oolitic Period.]

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 cuira.s.sed 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."

[Ill.u.s.tration: Fig. 119.--Ramphorynchus restored. One-quarter natural size.]

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 cuira.s.s both on the back and belly. In order to show this peculiarity, a living individual is represented on the sh.o.r.e, and a dead one is floating on its back in shallow water, leaving the ventral cuira.s.s exposed.

Behind the _Teleosaurus cadomensis_ in the engraving, another Saurian, the _Hylaeosaurus_, 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 cla.s.s 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. Puzosia.n.u.s_. 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.

[Ill.u.s.tration: Fig. 120.--Eryon arctiformis.]

[Ill.u.s.tration: Fig. 121.--Perfect Ammonite.]

Among the Echinoderms, _Cidaris glandiferus_, _Apiocrinus Roissya.n.u.s_, and _A. rotundus_, the graceful _Saccocoma pectinata_, _Millericrinus nodotia.n.u.s_, _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 ca.n.a.l, with the hollow lenticular s.p.a.ces 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 Wilts.h.i.+re, Abbotsbury in Dorset, at Soissons, and Roch.e.l.le. This species--known as the Bradford Pear-Encrinite--is only found in the strata mentioned.

[Ill.u.s.tration: XIX.--Fig. 1.--Apiocrinites rotundus. Fig. 2.--Encrinus liliiformis.]

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.