ROO 



ROS 



aHd tertiary in arrangement, deposited 

 by water and stratified in form. 



3. The Volcanic Rocks are of most 

 recent arrangement, composed of volcanic 

 matter, and unstratified in form. 



Other classification. Rocks may be 

 arranged' into four groups or classes, 

 dependent chiefly upon their relative po- 

 sition. 1. Granitic Rock, or those form- 

 ing the basis or foundation of the rest. 

 2. Stratified Rocks, divided, according to 

 the order of their deposition, into four 

 groups, viz. primary, secondary, tertiary, 

 and alluvial. 3. Overlying or interjected 

 rocks, so named because they appear lying 

 over, or interspersed among, the stratified 

 rocks. 4. Volcanic rocks, of the same 

 nature as the last, but produced by vol- 

 canoes at present or recently in 'action. 

 The first, third, and fourth classes are 

 all unstratified. 



ROCK BUTTER. Alum mixed with 

 alumina and oxide of iron, oozing out of 

 rocks which contain alum. 



ROCK CRYSTAL. A pure crystal- 

 lized variety of quartz, of which the 

 Scotch cairngorm is a variety. The pur- 

 ple-coloured rock-crystals are commonly 

 called amethysts, and the yellow-coloured 

 have the name of topazes. See Corundum. 



ROCK SALT. Common culinary salt, 

 or chloride of sodium, occurring in vast 

 solid masses or beds, in different forma- 

 tions, extensively in the New Red Sand- 

 stone formation, as in Cheshire ; in this 

 condition it is called rock salt. 



ROCK WOOD. A variety of asbestus, 

 of a brown colour, and with the appear- 

 ance of wood ; found in the Tyrol, &c. 



RODE'NTIA {rodo, to gnaw). Glires. 

 An order of Mammalia, in which the 

 jaws are deficient in true incisors, their 

 places being supplied by the canines, 

 which are brought forward, and adapted 

 to gnawing, as in the beaver, the rat, the 

 hare. 



ROESTONE. A variety of compact 

 limestone, called Bath-stone, Ketton- 

 stone, Portland-stone, and Oolite ; it is 

 used for building, but is porous and apt 

 to moulder away. 



ROMA'NZOVITE. A species of gar- 

 net, found in Finland. 



ROOT. The square root of any num- 

 ber, as 16, is a number which, when mul- 

 tiplied by itself, produces 16. The cube 

 root of any number, as 27, is a number 

 which, when multiplied by itself twice, 

 produces 27. The fourth, fifth, kc. roots 

 are numbers which, when multiplied 

 three, four, &c. times, produce the ori- 

 290 



ginal numbers. The mark ^ is the 

 radical sign, or sign of the root, being 

 the first letter of the Latin term radix, 

 a root. Hence — 



^ 16is4; for4 X 4 = 16 



3y 27 is 3 ; for 3 X 3 X 3 = 27 



^^ 16 is 2 ; for 2 X 2 X 2 X 2 =16. 



Root of Equation. In equations the 

 unknown quantities have particular 

 values, -which are sometimes called the 

 *' roots" of the equations, and are said to 

 satisfy them. Thus, if X' = 4, we know 

 that a; = 2 or — 2 ; and 2, — 2, are called 

 the roots of the equation x"^ = 4. 



ROOT OF PLANTS. The descend- 

 ing part of the axis of plants, or that 

 portion which tends towards the cen- 

 tre of the earth. The main body is 

 called the caudex, its minute divisions 

 being called radicles or fibrils. When a 

 root is divided into many fibrils, it is 

 termed z. fibrous root ; when truncated at 

 the extremity, prcemorse ; when it tapers 

 conically downward, it is termed fusi- 

 form, or tap-rooted. Under the general 

 term root, many parts have been erro- 

 neously enumerated, as subterranean 

 stems, the tuber, the cormus,&c. 



ROSA'CEiE. The Rose tribe of dico- 

 tyledonous plants. Herbaceous plants 

 and shrubs with leaves alternate; flowers 

 polypetalous; stowera* perigynous ; ovaria 

 superior, solitary, or several ; fruit 1-seed- 

 ed nuts, or acini, or follicles containing 

 several seeds. 



ROSCHGEWaCHS. The name given 

 by the Hungarian miners to the sulphur- 

 salt commonly called brittle vitreous 

 silver. It appears to be composed of the 

 same constituent elements as the dark 

 and the bright red ruby- silver ores, but 

 in different proportions. 



ROSE or MILK QUARTZ. A sub- 

 species of indivisible quartz, of rose-red 

 and milk-white colours. It is probably 

 silica, coloured with manganese. It oc- 

 curs in Bavaria in beds of quartz in 

 granite. 



ROSELITE. A new mineral of a deep 

 rose colour, found on amorphous greyish 

 quartz in Saxony. It is an arseniate of 

 cobalt, with lime and magnesia. 



ROSTRUM. Literally, a beak; and 

 hence, applied in Botany to any rigid 

 prolongation of considerable length. 

 Rostellum, a diminutive of rostrum, is 

 also employed to denote any small beak- 

 shaped process. 



RO'SULATE {rosa, a rose). In bota- 

 nical nomenclature, this term is used 

 to designate parts wbj,^h are not oppo- 



