ONYCHIA 



Onychia ((Jr.. onyx, finger-nail). 



Inllaiiiination of the U-d of t he nail. 



It may l>e due to direct m(. 



or may develop in the course of 

 (Hsosnrn of the akin auch as eczema 

 mid psoriasis. 



Onyx. < ienerul term applied to 

 rilmnd agates characterised by 

 ui-ll defined alternate rings of pure 

 milk -white with bands of other 

 colour--. If the tint of the secondary 

 rings is flesh colour, the agate ia 

 known as rh dccdony-onyx ; if red, 

 carnelian-onyx ; if green, sardonyx. 

 All these are utilised for intaglios 

 (incised) and cameos (relief) carv- 

 i jewelry. 



<>n\\ opal is a natural atone 

 built up of alternate layers of 

 precious and common opal. < >nv\ 

 maiMo, from Mexico, and onyx 

 alabaster, from Egypt, are hand- 

 some forms of stalactite marble, 

 mostly calcite. They are some- 

 times used for ornamental pur- 

 poses. See Gem. 



Oodnadatta. Township in 

 South Australia. It is 688 m. from 

 Adelaide and since 1891 has been 

 the railhead of the transcontinental 

 rly. to Darwin, 1,350 m. distant in 

 Northern Territory. Mount Bras- 

 sey, 500 m. distant in the Mac- 

 donell Ranges, is reached from 

 Oodnadatta by camel transport, 

 j by which means its mica produce 

 I is brought to railhead for export. 



Oolite (Gr., don, egg ; litfios, 

 \ stone). In geology, name given to 

 the upper and middle division of 

 the Jurassic rocks. During this 

 period of geological time the 

 continents of Europe and Asia 

 were covered to a large extent by 

 the ocean, and the Oolite deposits 

 are chiefly limestones formed by 

 the fossil remains of marine 

 animals. The Jura mountains of 

 Switzerland are typical examples. 



Great Oolite is the name given to 

 rocks of the Oolite System, and 

 sometimes called Bath Oolite from 

 their typical occurrence at Bath. 

 Great Ooliterocks arefound in Wilt- 

 shire, Somersetshire, Gloucester- 

 shire, etc., and provide the well- 

 known building stones, Bath stone, 

 S 1 01 test ic Id slate, etc. They contain 

 , a number of fossils of dinosaurs, 

 pterosaurs, etc. 



Inferior Oolite is named from 

 its occurrence in strata beneath 

 the Great Oolite. The rocks, found 

 in various parts of Great Britain, are 

 limestones, calcareous sandstones, 

 ironstones, slates, etc., and contain 

 many valuable coal seams. The 

 Collyweston slates are famous 

 roofing slates, and many of the 

 Inferior Oolite rocks make excel- 

 lent building stones. The rocks 

 contain a large number of fossils, 

 including cycads, and conifers. i>ee 

 Jurassic System. Prow, o-olite. 



5849 



Oology ((Jr. 6i'm, egg). Branch 

 of ornithology which deals with 

 the eon of bird*. All bird*' eggs 

 are alike in the general arrange- 

 ment of their content* and in tin- 

 chalky nature of the ahell ; but 

 differ widely in size, colour, and 

 shape. The largest known egg is 

 that of the extinct AepyornU of 

 Madagascar, which contained about 

 two gallons, while the smallest are 

 those of certain humming birds. 

 See Bird ; Egg, colour plate ; 

 Embryology. Pron. o-ology. 



Hibiiography. Coloured lllustru 

 tiona of Eggs of British Birds. W. 

 C. Hewitaon, 3rd ed. 1856 ; British 

 Nesta, Eggs, and Egg Collecting. 

 R. Kearton.1890 ; Nests and KRKH 

 of British Birds, F. O. Morris, rev. 

 W. B. Tegetmeier, 4th ed. 1896 ; 

 Coloured Figure* of the Eggs of 

 British Birds. H. Soel.ohm. 1896. 



Oosterhout. Town of the 

 Netherlands, in the pror. of N. 

 Brabant. It lies 5 m. N.E. of Breda, 

 with which it has tramway con- 

 nexion. Situated in flat agri- 

 cultural country, it has a consider- 

 able trade in local produce, and 

 industries in tiles, pottery, sugar - 

 refining, and tanning. Pop. 12,000. 



Ootacamund. Hill station of 

 Madras Presidency, India, in 

 Nilgiris dist. It is the finest hill 

 station in India, being over 7,000 

 ft. in alt., and having a temperate 

 climate, with night frosts in Dec. 

 and Jan. Around the station, where 

 eucalyptus and wattle grow in pro- 

 fusion, are the open, rolling downs 

 of the Nilgiri Hills, the home of the 

 Ootacamund Hunt. Here the 

 Madras Government sits during 

 the hot season ; the government 

 offices on Stonehouse Hill date 

 from 1821, and Government House 

 from 1876. The station is reached 

 by a branch line from Podanur. 

 Pop. 18,800. 



Ooze. Name given to the de- 

 posits of calcareous mud on the 

 ocean bed at great depths, com- 

 posed mainly ofthe external skele- 

 tons of minute Protozoa. These 

 deposits through vast ages have 

 built up the chalk cliffs and 

 hills. The animals belong largely 

 to the order Thalamophora, better 

 known as Foraminifera. As Globi- 

 gerina is one of the commonest 

 forms, the mud is often known as 

 Globigerina Ooze. These minute 

 animals swarm near the surface 

 of the sea, and as they die their 

 skeletons fall in a constant rain 

 of impalpable matter to the depths. 



At greater depths the ooze con- 

 sists of the flinty skeletons of Radi- 

 olaria, another order of minute 

 Protozoa. The reason is that the 

 enormous pressure causes the water 

 to hold in solution great quantities 

 of carbonic acid, which dissolves 

 the chalky skeletons of the Thal- 



OPAU 



amophora, while the flinty skele- 

 tons of the Kadiolaria are leas 

 affected. Radiolaiian Ooze is 

 usually met with beyond the 4,000 

 fathom line. Set Foraminifera. 



O.P. AMin-v. in stage direc- 

 tions for opposite prompt side. 

 The O.P. (old prices) riot* occurred 

 Sept. 18-Dec. 16, 1809, when 

 Covent Garden Theatre, London, 

 was reopened by J. P. Kemble, 

 with increased prices of nil mission 

 The old prices were restored after 

 Mm. h damage had been done. 



The O.P. (Old Playgoers') Club 

 was founded in 1900, by Carl 

 Henschell, to provide a meeting- 

 place for regular " first-nighters " 

 and other theatrical enthusiasts. 

 Lectures, concerts, and dinners are 

 given occasionally by the club, 

 which possess PS a collection of orer 

 10.000 playbills. Its premises are 

 in 1-4, John Street, Adelphi, W.C. 



Opal. In mineralogy, a hydrous 

 dioxide of silicon. It is amorphous 

 or non-crystalline, contains a very 

 variable quantity of water, and 

 varies in colour from dark to pale 

 yellow, red, blue, or green, the 

 lighter colours being more common. 

 The mineral is a secondary one, re- 

 sulting from the decomposition of 

 the primary ingredients of felspars, 

 etc. It is often found in volcanic 

 rocks, and the variety known as 

 wood opal is petrified fossil wood, 

 the structure of which is preserved 

 while the colours are opalescent. 

 The mineral has the power of 

 penetrating organic remains, fossil 

 shells, etc. 



The precious opal has been 

 from time immemorial one of the 

 best known gems, and in ancient 

 times it was considered to bring 

 its wearer good fortune. It is a 

 semi-transparent, semi-transluc- 

 ent stone, bluish or yellowish 

 white in colour as a rule, and show- 

 ing a wonderful play of all colours 

 of the rainbow as the light strikes 

 it at various angles. This play of 

 colour is due to the tiny fissures 

 filled with air and water. 



Precious opal is found in Czecho- 

 slovakia, S. America, New South 

 Wales, th U.S.A., etc. The opal- 

 escence is best brought out by 

 giving the gem a rounded polished 

 surface, and the loss of colour is due 

 to the surface wearing, the stone 

 being a comparatively soft one. 

 The fire opal, a beautiful red stone, 

 with yellow, or yellow and green 

 reflections, is found in Mexico ; as 

 is the girasol, a bluish white opal, 

 with red reflections. Hyalite (q.v.) 

 is a glassy variety of the mineral 

 without any opalescence, and 

 hydrophane is another variety of 

 porous texture which becomes 

 transparent on immersion in water. 

 Menilite is a variety found in 



