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ONYX

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Originally appearing in Volume V20, Page 120 of the 1911 Encyclopedia Britannica.
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ONYX , a banded See also:

chalcedony or striped See also:agate, composed of See also:white layers alternating with others of See also:black, See also:brown or red See also:colour. A typical onyx consists of two or more black and white strata, whilst the See also:term See also:sardonyx is applied to the See also:stone if it contains red or brown bands (see SARDONYX). Probably those varieties which show red and white zones originally suggested the name " onyx," from Gr. 6vu (a See also:finger See also:nail), since the See also:colours of such stones may be not unlike those of the nail. The onyx when worked by the See also:lapidary was often designated by the diminutive 6vI ov; and at the See also:present See also:day the term nicolo, a corruption of the See also:Italian diminutive onycolo, is applied to an onyx which presents a thin layer of chalcedony deriving a bluish tint from the subjacent black ground. The See also:Hebrew See also:soham is translated in the authorized version of the Old Testament " onyx," but the revised version gives in some of the passages an alternative marginal See also:reading of " See also:beryl." The position of the See also:land of Havilah, which yielded the onyx-stone, is uncertain. See also:India has for ages supplied the finest onyxes, and hence jewellers apply the expression " See also:Oriental onyx " to any stone remarkable for beauty of colour and regularity of stratification, quite regardless of its locality. As far back as the 1st See also:century the author of the Periplus See also:Maris Erythraei mentions the onyx among the products of Plythanae, a locality probably identified with Paithan on the See also:Godavari; and he further states that the stones were taken down to Barygaza, the See also:modern See also:Broach, where the agate See also:trade still flourishes. It is probable that the See also:early Greeks and See also:Romans derived their prized agate-cups from this locality. The See also:Indian onyx is found, with agate and See also:jasper-pebbles, in See also:river gravels derived from the disintegration of the amygdaloidal volcanic rocks of the See also:Deccan. A See also:great See also:deal of onyx now sold is obtained from See also:South See also:American agates, cut in See also:Germany. It often happens that the See also:lower deposits in an agate-nodule are in See also:horizontal layers, forming onyx, while the other deposits have adapted themselves to the curved contours of the cavity.

The onyxes cut from agate-nodules are usually stained artificially, as explained under AGATE. The onyx is largely used for beads, brooches, pins, See also:

ring-stones and other small ornamental See also:objects, while the larger pieces are occasionally wrought in the See also:form of cups, howls, vases, &c. Onyx is the favourite stone for See also:cameo See also:work, See also:advantage being taken of the differently-coloured layers to produce a subject in See also:relief on a background of another colour. For See also:fine examples of See also:ancient cameo-work in onyx and sardonyx see See also:GEM. It should be noted that the term onyx, or onychite, was formerly, and is still sometimes, applied to certain kinds of banded See also:marble, like the " oriental See also:alabaster " (see ALABASTER). Such substances are quite distinct from the hard siliceous onyx, being much softer and less See also:precious: they are, in fact, usually deposits of See also:calcium carbonate like stalagmite and travertine. The ornamental stones known as Mexican onyx, or Tecali marble, and Algerian onyx are of this See also:character; and in See also:order to avoid any confusion with the true onyx it is well to distinguish all the calcareous " onyxes " as onyx-marble. The well-known " See also:Gibraltar stone " is an onyx-marble, with brown bands, from caverns in the See also:limestone of Gibraltar. The Tecali onyx, some-times with delicate See also:green shades, takes its name from the See also:district of Tecali; one of its localities being La Pedrara, about 21 M. from the See also:city of See also:Puebla. For onyx-See also:marbles see Dr G. P. See also:Merrill, See also:Rep.

U.S. Nat. See also:

Mus. for 1893 (1895), P. 539. (F. W. R.*) 00LITE (Gr. g3ov, See also:egg, XLBos, stone), in See also:geology, a term having two distinct meanings. In See also:petrology (q.v.) it denotes a type of See also:rock structure characterized by the presence of See also:minute spherical grains resembling the See also:roe of a See also:fish; if the grains become larger, the structure is said to be pisolitic (Gr. irtaos, See also:pea). In stratigraphical geology, the oolite is a See also:division of the See also:Jurassic See also:system (q.v.). The term appears to have been first applied in this latter sense by A. J. M.

Brochant de See also:

Villiers in 18o3, and through the labours of W. See also:Smith, W. D. See also:Conybeare, W. See also:Buckland and others, it was gradually introduced for the calcareous rocks of the See also:British Jurassic until it came to comprehend the whole system above the See also:Lias. See also:Custom still sanctions its use in See also:England, but it has been objected that the Oolitic (Jurassic) system contains many strata that are not oolitic; and since oolitic structure occurs in limestones of all ages, it is misleading to employ the word in this way. The oolites are usually divided into: the Upper or See also:Portland Oolite, comprising the Purbeck, Portland and Kimeridge stages; the See also:Middle or See also:Oxford Oolite, including the See also:Corallian, See also:Oxfordian and Kellaways beds; and the Lower Oolites, with the See also:Cornbrash, Great or See also:Bath Oolite (Bathonian), Fullonian and the Inferior Oolite (See also:Bajocian). The Great Oolite and Inferior Oolite are treated here. The Inferior Oolite, called by See also:William Smith the " Under Oolite " from its occurrence beneath the Great or " Upper Oolite " in the neighbourhood of Bath, received its present name from J. Townsend in 1813. It is an extremely variable assemblage of strata. In the Cotteswold Hills it is a See also:series of marine deposits, 264 ft. thick near See also:Cheltenham, but within 25 M. the strata thin out to 30 ft. at Fawler in See also:Oxfordshire.

A typical See also:

section N.E. of Dursley contains the following subdivisions: o a~ S. White Freestone .5 ft. oo °'}l Clypeus Grit . . . 6-15 ft. Cosmoceras See also:Parkin- 0- It, b.O v p° to. ( Upper Trigonia Grit 2-12 ft. a o Gryphite Grit . 2-12 ft. Ste hanoceras ,.,.1 LowerTrigonia Grit .2-12 ft. Hhanoce phriesianum. Upper Freestone .

6-2o ft. c Oolite See also:

Marl . . 5-10 ft. gal ° Lower Freestone 45-130 ft. c.a.; Pea Grit . 3-20 ft. Murchisonae. a 3 is a~ {Lower Limestone 10-25 ft. at, . oo Cephalopod Limestones-7 ft. Lioceras opalinum. s Cotteswold Sands 10-120 ft. J Lytoceras jurense.

The basal sandy series, which is closely related with the underlying Lias, is usually described as the Midford Sands (from Midford, near Bath), but it is also known locally as the See also:

Bradford, See also:Yeovil or Cotteswold Sands. The Pea Grit series contains pisolitic limestone and coarse, See also:iron-stained oolite and sandy limestone. The freestones are compact oolite See also:lime-stones. The ragstones are fossiliferous, earthy and iron-stained oolitic limestones. The " grits " are really coarse-grained limestones or calciferous sandstones. Between Andoversford and Bourton-in-the-See also:Water the Inferior Oolite is represented by ragstones (Ferruginous beds, Clypeus Grit, Trigonia See also:bed, Notgrove Freestone, Gryphite Grit) and freestones (Upper Freestones and Harford Sands, Oolite Marl, Lower Freestone). Near Chipping See also:Norton in Oxfordshire the " Chipping Norton Limestone " lies at the See also:top of a very variable series of rocks. In Rutlandshire, See also:Northamptonshire and See also:Lincolnshire the following beds, in descending order, belong to the Inferior Oolite: Lincolnshire limestone (shelly, See also:coral-bearing and oolitic), Collyweston See also:slate, Lower Estuarine series and See also:Northampton Sands (hard calcareous sandstones, See also:blue and greenish ironstones and sandy limestones). The Collyweston slates are arenaceous limestones which have been used for roofing slates since the See also:time of See also:Henry VII.; See also:Easton, Dene and See also:Kirkby are important localities. The fissility of the rock is See also:developed by exposure to See also:frost. Similar beds are the Whittering Pendle and White Pendle or Duston slate. The Inferior Oolite of See also:Yorkshire differs from that of the Cotteswold district; in See also:place of the marine limestones of the latter See also:area there is a thick series of sands and sandstones withshales and beds of See also:coal; these deposits are mainly estuarine with occasional marine beds.

The See also:

principal subdivisions, in descending order, are: the See also:Scarborough or See also:Grey Limestone series, the Middle Estuarine series with their coal seams; the Millepore series and Whitwell or See also:Cave Oolite; the Lower Estuarine series with the Eller See also:Beck bed and See also:Hydraulic Limestone; the Dogger and Blea Wyke beds. The last-named beds, like the Midford Sands, exhibit a passage between the Inferior Oolite and the Lias. In See also:Skye and Raasay the Inferior Oolite is represented by See also:sand-stones. The fossils of the Inferior Oolite are abundant. Over 200 See also:species of Ammonite are known; gasteropods are numerous: Trigonia, See also:Lima, Ostrea, Gerviliia, Pecten, are See also:common pelecypods; Terebratula, Waldheimia and Rhynchonelia are the prevailing brachiopods. See also:Corals are very numerous in some limestones (Isastrea, Montivaultia). Urchins are represented by Cidaris, Acrosalenia, Nucleolites, Pygaster, Pseudodiadema, Hemicidaris; See also:starfish by Solaster, Astropecten, and Crinoids by Pentacrinus, Apiocrinus. Plant remains, cycads, ferns, Ginkgo and coniferous trees are found most abundantly in the Yorkshire area. The economic products of the Inferior Oolite include many well-known See also:building stones, notably those of See also:Ham See also:Hill, Doulting, Dundry, Painswick, Cheltenham, Duston, See also:Weldon, Ketton, Barnack, See also:Stamford,Casterton, Clipsham, Great Ponton, Ancaster, Aislaby (Lower Estuarine series). Several of the stones are used for road See also:metal. Iron ores have been worked in the Grey Limestone, the Eller Beck bed, the Dogger and the Northampton beds, the latter being the most important. The Great or Bath Oolite is typically developed in the See also:neighbour-See also:hood of Bath, and except in a modified form it does not extend beyond the counties of See also:Wiltshire, See also:Somersetshire, See also:Gloucestershire and Oxfordshire.

It does not reach so far as Yorkshire, unless the Upper Estuarine series of that district is its representative. The principal subdivisions of the series are: Wiltshire, Somersetshire, Northamptonshire, Gloucestershire, Oxfordshire. . f B ordhir rdshire Lin , Lincolnc In Beds hire. a False - bedded Oolites = Great Oolite See also:

Clay = Blis- Q. See also:Kemble beds, " White See also:worth Clay. Limestone, " See also:pale, earthy Limestones, occasionally oolitic, and Marls. Upper Ragstones of Bath. False - bedded Oolites =the Great Oolite Limestone principal ncipal building stones, (generally non-oolitic). Freestone." Fissile calcareous Sandstones; Upper Estuarine series o oolitic Limestones and Thickness, 20-100 ft. See also:Clays ; Lower Ragstones of Bath and Stonesfield Slate. Thickness, 100-130 ft. An exact correlation of the Great Oolite strata in the N.E. area with those of the S.W. is not possible on See also:account of the great variability and impersistence of the beds.

Current bedding is very prevalent, and See also:

minor stratigraphical breaks are common. The See also:absence of the typical Great Oolite from the N.E. district is probably due in See also:part to contemporaneous erosion with overstep of the succeeding formation, and in part to See also:local changes in the sediment in the shallow See also:waters of this See also:epoch. This may also explain the rapid thinning-cut of the Great Oolite south of Bath, where its place may be taken, to some extent, by the Bradford Clay, See also:Forest Marble and Y01m-See also:dam. The Great Oolite is not readily divisible into palaeontological zones, but the ammonite Perisphinctes arbustigerus may be taken as the characteristic form along with Belemnites bessinus and Terebratula maxillata. Corals (Isastraea, Thamnastria) and See also:Polyzoa (Stomatopora, Diastopora) are abundant. Hemicidaris, Cidaris, Acrosalenia, Clypeus and other urchins are common: Pentacrinus and A piocrinus represent the Crinoids. Terebratula, Rhynchonella, Waldheimia, Crania are the prevailing brachiopods ; the common pelecypods, Pecten, Ostrea, Lima, Trigonia, Modiola; Natica, Nerinea and other gasteropods are found.- Perisphinctes grandes, Macrocephalites subcontractus, Oppelia See also:discus and See also:Nautilus dispansus are among the more common cephalopods. The remains of fish (Mesodon, Hybodus), crocodiles (Teliosaurus), dinosaurs (Cetiosaurus, See also:Zone Fossils. 0 '4 d v v0 Harpocesas Megalosaurus), pterosaurs (Rhamphocephalus), and in the Stonesfield slate the jaws of marsupial mammals (Amphctherium, Amphilestes, Phascolotherium) occur. The building stones of the Great Oolite are mainly oolitic freestones, viz. the varieties of " Bath stone " quarried and See also:mined in the neighbourhood of that city (Corsham Down, Monks See also:Park, Coombe Down, See also:Odd Down, See also:Box Ground, &c.) and more shelly limestones like the Taynton and See also:Milton stone. The Stonesfield slate has been largely worked near See also:Woodstock in Oxfordshire and in Gloucestershire for roofing, &c. The " slates " are brown calcareous See also:sandstone, grey and slightly oolitic calcareous sand-stone, and blue and grey oolitic limestone.

A curious modification of the Great Oolite—White Limestone division—is characterized by irregular ramifying tubular cavities, usually filled with ochreous material; this rock occurs in blocks and layers, and is used for rockeries under the name of " Dagham stone " from Dagham Down See also:

north of See also:Cirencester. (See also JURASSIC.) (J. A.

End of Article: ONYX

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