JURASSIC SYSTEM_Encyclopaedia Britannica, 11th Edition, "Joints" to "Justinian I." Volume 15, Slice 5

+---------------------+----------------+---+---------+------+---------------------------+----------------------------------------+

| | | O | Sub- | | | |

| | | p | stages | Von | A. de Lapparent, | |

| | | e | Quen- | | | |

| | | l | stedt | | | |

+---+---+-------------+----------------+---+---------+------+------------+----------+---+----------------------------------------+

| | U | | Perisphinctes | | | | Purbeckien | | | \ |

| | p | Purbeckian | transitorius | | | U | or | | | | |

| | p | | | | | p | Aquilonien | | | | |

| | e +-------------+ | | | p +------------+ Port- | | | |

| | r | | Perisphinctes | | | e | | landien | N | | |

| | O | | Olcostephanus | | | | | | o | | |

| | o | | gigas | | | o | | | j | | Ammonitico |

| | l +-------------+ | | | r +------------+----------+ u | | rosso of \ _Acanthicus_ |

| | s | | tenuilobata | M | | i | Pteroceran | | s | | | |

| +---+-------------+ | a | | t +------------+----------+ i | | | |

| | M | Corallian | Peltoceras | l | [beta] | e | Astartien | Sequa- | q | | | |

| | i | | bimammatum | m | | | Rauracien | nien | u | | | |

| | d +-------------+ | | | J +------------+----------+ e | | | |

| | d | | Peltoceras | | | u | Argovien | | | | | |

| O | e | | Aspidoceras | | | a | Neuvizien | dien | | > Kalke and |

| L | O +-------------+ | | +------+------------+----------+ | | |

| I | o | | Peltoceras | | | | | | | | |

| S | t | | Jason | | | M | Lower | | | | |

| | e | | Macrocephalites| | | i | Divesien | | | | |

| | s | | macrocephalus | | | d | | | | | |

| +---+-------------+ +---+ | d +------------+----------+ | | Posidonien Beds|

| | w | | ferruginea | | | o | | | / |

| | e +-------------+ | | | r +------------+ | |

| | r | | Parkinsonia | | | | | M | |

| | | | Parkinsoni | D | | B | | é | |

| | O | | Coeloceras | o | | r | | s | _Sauzei_-Kalke |

| | o | Bajocian | Humphresianus | g | | o | | o | |

| | l | (Inferior | Sphæroceras | g | | w | Bajocien | j | |

| | i | Oolite) | Sauzei | e | | n | | u | |

| | t | | Sonninia | r | [delta] | | | r | |

| | e | | Sowerbyi | | [gamma] | J | | a | |

| | s | | Harpoceras | | [beta] | u | | s | |

| | | | Murchisonae | | | r | | s | Oolite of San |

+---+---+-------------+----------------+ | | a +------------+ | i | Vigilio |

| | | opalinum | | | | | | e | |

+---+-----------------+----------------+---+---------+------+ | | | |

| +-----------------+ | | | +------------+ | | \ |

| | | Amaltheus | | | L | | | | | | |

| | | margaritatus | | | o | | | | | | |

| | | Phylloceras | | [gamma] | r | | | | > ter | | |

| | | ibex | L | | | | | É | | Kalke| | |

| | | Aegoceras | i | | o | | | o | | | | \ |

| | | Jamesoni | a | | r | | | j | | | Brachio- | Algäu | |

| L +-----------------+ | s | | +------------+ | u | | > pod or > Beds | |

| I | | Arietites | | [beta] | B | | S | r | \ | | Hierlatz| | |

| A | | raricostatus | | | l | | y | a | | / | facies | | |

| S | | Oxynoticeras | | | a | | s | s | | | | | Flec- |

| | | oxynotum | | | c | | t | s | | | / > ken- |

| | | Arietites | | | k | | è | i | | | | mergel|

| | Lower Lias | obtusus | | | | | m | q | | | | |

| | | Arietites | | | J | | e | u | | | | |

| | | Bucklandi | | | u | | | e | | Gres- | | |

| | | Schlotheimia | | | r | | L | | > tener | | |

| +-----------------+----------------+---+---------+ | (part) | s | | | / |

| | | | | | | Hettangien | i | | | |

| | | | | | | (part) | q | | | |

| | | | | | | Rhétien | u | | | |

| | | | | | | |Lias | | / |

+---+-----------------+----------------+---+---------+------+------------+----------+---+----------------------------------------+

_Life in the Jurassic Period._--The expansion of the sea during this

period, with the formation of broad sheets of shallow and probably

warmish water, appears to have been favourable to many forms of marine

life. Under these conditions several groups of organisms developed

rapidly along new directions, so that the Jurassic period as a whole

came to have a fauna differing clearly and distinctly from the

preceding Palaeozoic or succeeding Tertiary faunas. In the seas, all

the main groups were represented as they are to-day. Corals were

abundant, and in later portions of the period covered large areas in

Europe; the modern type of coral became dominant; besides

reef-building forms such as _Thamnastrea_, _Isastrea_, _Thecosmilia_,

there were numerous single forms like _Montivaltia_. Crinoids existed

in great numbers in some of the shallow seas; compared with Palaeozoic

forms there is a marked reduction in the size of the calyx with a

great extension in the number of arms and pinnules; _Pentacrinus_,

_Eugeniacrinus_, _Apiocrinus_ are all well known; Antedon was a

stalkless genus. Echinoids (urchins) were gradually developing the

so-called "irregular" type, _Echinobrissus_, _Holectypus_,

_Collyrites_, _Clypeus_, but the "regular" forms prevailed, _Cidaris_,

_Hemicidaris_, _Acrosalenia_. Sponges were important rock-builders in

Upper Jurassic times (_Spongiten Kalk_); they include lithistids such

as _Cnemediastrum_, _Hyalotragus_, _Peronidella_; hexactinellids,

_Tremadictyon_, _Craticularia_; and horny sponges have been found in

the Lias and Middle Jurassic.

Polyzoa are found abundantly in some of the beds, _Stomatopora_,

_Berenicia_, &c. Brachiopods were represented principally by

terebratulids (_Terebratula_, _Waldheimia_, _Megerlea_), and by

rhynchonellids; _Thecae_, _Lingula_ and _Crania_ were also present.

The Palaeozoic spirifirids and athyrids still lingered into the Lias.

More important than the brachiopods were the pelecypods; _Ostrea_,

_Exogyra_, _Gryphaea_ were very abundant (Gryphite limestone, Gryphite

grit); the genus _Trigonia_, now restricted to Australian waters, was

present in great variety; _Aucella_, _Lima_, _Pecten_, _Pseudomonotis_

_Gervillia_, _Astarte_, _Diceras_, _Isocardia_, _Pleuromya_ may be

mentioned out of many others. Amongst the gasteropods the

_Pleurotomariidae_ and _Turbinidae_ reached their maximum development;

the Palaeozoic _Conularia_ lived to see the beginning of this period

(_Pleurotomaria_, _Nerinea_, _Pteroceras_, _Cerithium_, _Turritella_).

Cephalopods flourished everywhere; first in importance were the

ammonites; the Triassic genera _Phylloceras_ and _Lytoceras_ were

still found in the Jurassic waters, but all the other numerous genera

were new, and their shells are found with every variation of size and

ornamentation. Some are characteristic of the older Jurassic rocks,

_Arietites_, _Aegoceras_, _Amaltheus_, _Harpoceras_, _Oxynoticeras_,

_Stepheoceras_, and the two genera mentioned above; in the middle

stages are found _Cosmoceras_, _Perisphinctes_, _Cardioceras_,

_Kepplerites Aspidoceras_; in the upper stages _Olcostephanus_,

_Perisphinctes_, _Reineckia_, _Oppelia_. So regularly do certain forms

characterize definite horizons in the rocks that some thirty zones

have been distinguished in Europe, and many of them can be traced even

as far as India. Another cephalopod group, the belemnites, that had

been dimly outlined in the preceding Trias, now advanced rapidly in

numbers and in variety of form, and they, like the ammonites, have

proved of great value as zone-indicators. The Sepioids or cuttlefish

made their first appearance in this period (_Beloteuthis_,

_Geoteuthis_,) and their ink-bags can still be traced in examples from

the Lias and lithographic limestone. Nautiloids existed but they were

somewhat rare.

A great change had come over the crustaceans; in place of the

Palaeozoic trilobites we find long-tailed lobster-like forms,

_Penaeus_, _Eryon_, _Magila_, and the broad crab-like type first

appeared in _Prosopon_. Isopods were represented by _Archaeoniscus_

and others. Insects have left fairly abundant remains in the Lias of

England, Schambelen (Switzerland) and Dobbertin (Mecklenburg), and

also in the English Purbeck. Neuropterous forms predominate, but

hemiptera occur from the Lias upwards; the earliest known flies

(Diptera) and ants (Hymenoptera) appeared; orthoptera, cockroaches,

crickets, beetles, &c., are found in the Lias, Stonesfield slate and

Purbeck beds.

Fishes were approaching the modern forms during this period,

heterocercal ganoids becoming scarce (the _Coelacanthidae_ reached

their maximum development), while the homocercal forms were abundant

(_Gyrodus_, _Microdon_, _Lepidosteus_, _Lepidotus_, _Dapedius_). The

Chimaeridae, sea-cats, made their appearance (_Squaloraja_). The

ancestors of the modern sturgeons, garpikes and selachians, _Hybodus_,

_Acrodus_ were numerous. Bony-fish were represented by the small

_Leptolepis_.

So important a place was occupied by reptiles during this period that

it has been well described as the "age of reptiles." In the seas the

fish-shaped Ichthyosaurs and long-necked Plesiosaurs dwelt in great

numbers and reached their maximum development; the latter ranged in

size from 6 to 40 ft. in length. The Pterosaurs, with bat-like wings

and pneumatic bones and keeled breast-bone, flew over the land;

_Pterodactyl_ with short tail and _Rhamphorhyncus_ with long tail are

the best known. Curiously modified crocodilians appeared late in the

period (_Mystriosaurus_, _Geosaurus_, _Steneosaurus_, _Teleosaurus_).

But even more striking than any of the above were the Dinosaurs; these

ranged in size from a creature no larger than a rabbit up to the

gigantic _Atlantosaurus_, 100 ft. long, in the Jurassic of Wyoming.

Both herbivorous and carnivorous forms were present; _Brontosaurus_,

_Megalosaurus_, _Stegosaurus_, _Cetiosaurus_, _Diplodocus_,

_Ceratosaurus_ and _Campsognathus_ are a few of the genera. By

comparison with the Dinosaurs the mammals took a very subordinate

position in Jurassic times; only a few jaws have been found, belonging

to quite small creatures; they appear to have been marsupials and were

probably insectivorous (_Plagiaulax Bolodon_, _Triconodon_,

_Phascolotherium_, _Stylacodon_). Of great interest are the remains of

the earliest known bird (_Archaeopteryx_) from the Solenhofen slates

of Bavaria. Although this was a great advance beyond the Pterodactyls

in avian characters, yet many reptilian features were retained.

Comparatively little change took place in the vegetation in the time

that elapsed between the close of the Triassic and the middle of the

Jurassic periods. Cycads, _Zamites_, _Podozamites_, &c., appeared to

reach their maximum; Equisetums were still found growing to a great

size and Ginkgos occupied a prominent place; ferns were common; so too

were pines, yews, cypresses and other conifers, which while they

outwardly resembled their modern representatives, were quite distinct

in species. No flowering plants had yet appeared, although a primitive

form of angiosperm has been reported from the Upper Jurassic of

Portugal.

The economic products of the Jurassic system are of considerable

importance; the valuable coals have already been noticed; the

well-known iron ores of the Cleveland district in Yorkshire and those

of the Northampton sands occur respectively in the Lias and Inferior

Oolites. Oil shales are found in Germany, and several of the Jurassic

formations in England contain some petroleum. Building stones of great

value are obtained from the Great Oolite, the Portlandian and the

Inferior Oolite; large quantities of hydraulic cement and lime have

been made from the Lias. The celebrated lithographic stone of

Solenhofen in Bavaria belongs to the upper portion of this system.

See D'Orbigny, _Paléontologie française_, _Terrain Jurassique_ (1840,

1846); L. von Buch, "Über den Jura in Deutschland" (_Abhand. d. Berlin

Akad._, 1839); F. A. Quenstedt, _Flötzgebirge Württembergs_ (1843) and

other papers, also _Der Jura_ (1883-1888); A. Oppel, _Die

Juraformation Englands, Frankreichs und s.w. Deutschlands_

(1856-1858). For a good general account of the formations with many

references to original papers, see A. de Lapparent, _Traité de

géologie_, vol. ii. 5th ed. (1906). The standard work for Great

Britain is the series of _Memoirs of the Geological Survey_ entitled

_The Jurassic Rocks of Britain_, i and ii. "Yorkshire" (1892); iii.

"The Lias of England and Wales" (1893); iv. "The Lower Oolite Rocks of

England (Yorkshire excepted)" (1894); v. "The Middle and Upper Oolitic

Rocks of England (Yorkshire excepted)" (1895). The map is after that

of M. Neumayr, "Die geographische Verbreitung der Juraformation,"

_Denkschr. d. k. Akad. d. Wiss., Wien, Math. u. Naturwiss._, cl. L.,

_Abth._ i, _Karte_ 1. (1885). (J. A. H.)

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