OOTACAMUND 



OPAL 



607 



Ootncaiiiiiiul, or UTAKAMAND, the chief 

 town iii the Neilgberry Hills (q.v.), the principal 

 sanatorium of the Madras Presidency, and the 

 summer headquarters of the governor of Madras. 

 It stands on a plateau, in an amphitheatre sur- 

 rounded by hills, 72-28 feet above the sea, 350 miles 

 from Madras city, and 24 from the nearest railway 

 station on the Madras line. There are a public 

 library ( 1859), the Lawrence Asylum ( 1858) for the 

 children of British soldiers, and Wanical gardens. 

 The mean annual temperature is 58 F. The first 

 house was built in 1821. Pop. 12,335. 



Oo/.C, a term technically applied to some kinds 

 of deposits found covering the liottom of the deeper 

 parts of the sea. It is not only the depth of the 

 water, but the distance from the land which deter- 

 mines the occurrence of ooze. As we pass from 

 the shore out to sea we find a succession of deposits, 

 shingle, sandy mud, mud all derived from the 

 land ; but at a distance varying from 00 to 300 

 nautical miles from the shore, and at a depth 

 of 2000 feet or more, lie the various oozes, which 

 consist of the remains of numerous small organ- 

 isms, but especially of the shells of Foraminifera. 

 A whitish deposit," containing enormous ntunben 

 of Glohigerina shells, which in dying have sunk 

 from the surface, is very widely distributed till 

 depths of about 2000 fathoms are approached. 

 There the Globigerina ooxe wanes away, and is 

 replaced in the deeper regions by so-called ' red 

 clay.' At the surface almve there are of course 

 here as elsewhere abundant Foraminifera which 

 still doubtless sink, but the physical conditions 

 of the great depths are such that their shells 

 are dissolved in falling. But in certain of the 

 deepest parts e.g. at 4.T7.) fathoms the Challenger 

 explorers found another kind of ooze, composed 

 of the flint shells of Kadiolarians. Resides this, in 

 other regions the shells of Pteropods and Diatoms 

 are abundant enough to form a characteristic oo/e. 



It is to l>e understood, however, that the various 

 oozes (Globigeiiiiii, Kadiolarian, Pteropod, Diatom, 

 &c. ) pass into one another, and that the names 

 usually express simply the predominance of one 

 or other kind of shell,' and also that the colours 

 wliite, yellow, brown, and red mainly denote the 

 proportion in which the 'red clay' is present. The 

 latter owes its colour to the oxides of iron and 

 manganese, and is composed of disintegrated mate- 

 rials of volcanic origin, such as pumice, and also 

 of meteoric dust. These, after being carried by 

 winds and floated on ocean currents, sink and are 

 distributed at the liottom. Hut as to the ooze in 

 the strict sense, it ought also to le noted that the 

 dead or dying organic material, which the rain 

 of these organisms brings to the bottom, serves 

 as the fundamental food supply of deep-sea animals, 

 while the shells not only accumulate as ooze, but 

 aid in the elevation of submarine volcano tops to 

 the level at which corals can grow. Finally, the 

 results of the ooze of incalculably distant ages are 

 teen in the chalk cliffs often obviously composed of 

 Foraminifera, or in snch Radiolarian deposits as 

 I: i liadoes Earth. See CHALK, DIATOMS, FORAM- 



IXIFERA, Gl.OnifiERINA, PTKI:OI')I> A, KADIOI.ARIA, 



SKA, and the concluding volume of the Challenger 

 Reports by Murray and Henard. 



OjaHt'. name given by petrologists to minute 

 black, opaque, amorphous aggregates, grains, and 

 patches of indeterminate mineral matter, which 

 are seen in manv igneous rocks when these are 

 viewed in thin slices under the microscope. Opa- 

 cite is probably in most eases hematite, limonite, 

 magnetite, or other iron oxide, and is a product 

 of the chemical alteration of one or other of the 

 original mineral constituents of the rock in which 

 it occurs. 



Opall. or KIXO-FISH (Lampris Itina), a fish of 

 the family Coryphoenidie or ' Dolphins,' order 

 Acanthopterygii. The body is compressed laterally 

 and deep, and is covered with small deciduous 

 scales. The cleft of the mouth is narrow, and 

 there are no teeth. The dorsal tin is single and 

 has no spinous portion ; the pectoral and ventral 

 fins are falciform and of nearly equal length. The 

 tail is forked. The lateral line has a strong curve 

 behind the head, and becomes straight about mid- 

 way between the eye and the root of the tail. This 

 fish is beautifully coloured ; the back is bluish 

 green ; the sides violet, becoming red underneath ; 

 round or oval silvery spots are scattered all over 

 the lx>dy ; the fins and tail are deep scarlet. It is 

 found only occasionally near shore. It prefers the 

 deeper waters of the North Sea, l>eing found oil' 



Opah (Lampris tuna). 



Norway, the British Isles, Iceland, Newfoundland, 

 and especially near the Azores and Madeira. It 

 is rare in the Mediterranean, and has not lieen 

 recorded off Greenland or east of the North Cape 

 in Norway. Specimens have been caught measur- 

 ing 6 feet in length ; one of 4 feet 5 inches weighed 

 140 Ib. The flesh is red or yellowish in colour, and 

 is excellent to eat. Its food, so far as is known, 

 consists of cuttle-fish and other ccphalopods. Other 

 names applied to it are Sun-fish (a name also applied 

 to Orthagoriscus and to the basking shark ), because 

 it comes to the surface of the water in calm 

 weather, Sea-pert, Carf, and Jerusalem Haddock. 



Opal, a mineral which differs from quartz in 

 containing generally 3 to 10 in some cases only 1, 

 in others as much as 21 per cent, of water, its only 

 other essential constituent being silica, although a 

 little alumina, oxide of iron, &c. is often present. 

 The water is readily driven off on the application 

 of heat, and some opals contain so small a propor- 

 tion of water that they might be descrilied simply 

 as jellifoi m quartz. Not infrequently minute scales 

 or plates of tiidymite (a crystallised variety of 

 silica) are present in opal. The latter is never 

 found crystallised, and does not exhibit a crystal- 

 line structure like quartz. It has a conchoidal 

 fracture, and is very easily broken. There are 

 many varieties, which pass into one another, so 

 that their precise limits cannot be defined, from 

 which has arisen no little confusion of names. The 

 finest kind is called Precious Opal or Noble Opal, 

 and sometimes Oriental Ojml. It is semi-trans- 

 parent or translucent, usually of a bluish or 

 yellowish white colour, yellow by transmitted light, 

 and exhibits a beautiful play of brilliant colours, 

 owing to minute fissures which refract the light. 

 It is much valued for setting in rings, brooches, 

 &c., and is polished with a convex surface, never 

 cut into facets, both because of its brittleness and 

 lw>cause its play of colours is thus best exhibited. 

 The ancients valued opals very highly. The 

 Roman senator Nonius preferred exile to giving 

 up an opal to Mark Antony. This opal was still 

 to lie seen in the days of Pliny, who ascribes to it 

 a value equal to more than 100,000 sterling. The 



