ROC 



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R O S 



slate in soft masses ; it is of a yel- 

 lowish-white colour ; a little unctuous to 

 the touch ; massive, tuberose, or stalac- 

 tical. It is mingled with clay and oxide 

 of iron. 



ROCK CRY'STAL. This, which is only the 

 most perfect variety of quartz, has, when 

 crystallized, received the name of rock 

 crystal: the same name has been ex- 

 tended to coloured crystals, when trans- 

 parent. The finest specimens of rock 

 crystal are found in Dauphine, in the 

 Alps, in Madagascar, &c. ; but it abounds 

 in every country, in all parts of the 

 world, in chasms or clefts of the oldest 

 rocks. The primitive form is a rhom- 

 boid of 94 15' and 85 45' ; the secon- 

 dary forms are an equiangular six-sided 

 prism, rather acutely acuminated on both 

 extremities by six planes which are set 

 on the lateral planes, a double six-sided 

 pyramid, an acute simple six-sided pyra- 

 mid, and acute double three-sided pyra- 

 mid. Splendent ; fracture perfect con- 

 choidal ; gives double refraction feebly. 

 Its specific gravity is from 2*5 to 2*8. 

 By friction it exhales a peculiar odour, 

 and some varieties also phosphoresce in 

 the dark. An analysis by Bergman gave 

 silex 93, alumine 6, lime 1. 



ROCK WOOD. A variety of asbestos of a 

 brown colour ; in its general appearance 

 greatly resembling fossil wood. 



ROCK CORK. The Bei-g kork of Werner ; 

 Suber montanum of Kirwan ; Asbeste 

 suberiform of Brongniart. Called also 

 Mountain cork ; a white or grey-coloured 

 variety of asbestus. Its specific gravity 

 varies from 0'68 to 0'99 : this, and its 

 fibrous structure, have obtained for it the 

 name of cork. Its constituents are silex 

 56-3, magnesia 26'2, lime 12-4, alumine 

 2*0, iron 3*1. It occurs in France, Ger- 

 many, and some other countries. Near 

 Alais, in France, it is met with on the 

 surface of the ground, in long white 

 masses, having a resemblance to human 

 bones. 



ROCK SALT. Common salt. This is found 

 in vast solid masses or beds, in different 

 formations, extensively in the new red 

 sandstone formation. The saliferous strata 

 of Northwich, form two beds of great thick- 

 ness, one being 120, the other 110 feet 

 in thickness. The origin of these beds 

 does not appear, to the present time, 

 to be satisfactorily understood or ex- 

 plained. 



RODE'NTIA. (from rodo, Lat. to gnaw.) 

 The fifth order of Mammalia. Called 

 also Gnawers. The order contains many 

 genera, some of which are familiar to us, 

 namely, the squirrel, the rat, the mouse, 

 the hare, the rabbit, &c. &c. From 

 the characters of their teeth, which are 



adapted neither for seizing nor tearing 

 their food, but merely to nibble and 

 gnaw it, they have received their name of 

 Roclents, or gnawers. The great ma- 

 jority of this order are gregarious, living 

 in burrows, in common habitations which 

 they excavate or fabricate themselves." 



ROE STONE. The roogenstein of Werner ; 

 oviform limestone of Kirwan. A name 

 given to the oolite, a variety of lime- 

 stone, from its being composed of small 

 rounded particles, resembling the roe or 

 eggs of a fish. See Oolite. 



ROSA'CE^E. An order of plants, including 

 the genera potentilla, fragaria, rosa, ru- 

 bus, spirasa, brayera, dryas, &c. &c. 

 The following is a description of this 

 order ; calyx with four or five teeth, the 

 odd one posterior or next the axis, with a 

 disk lining the tube, or surrounding the 

 orifice ; petals five, equal, perigynous ; 

 stamens indefinite in number, inserted 

 into the calyx within the petals ; ovaria 

 superior, sometimes solitary, one-celled, 

 either distinct, or, in some genera, co- 

 hering into a many-celled pistil, styles 

 lateral, and stigmata simple ; fruit either 

 a cynarrhodum, an etserio, or follicular ; 

 seeds suspended, embryo pointing to the 

 hilum, hardly any albumen ; herbaceous 

 plants or shrubs, leaves alternate, com- 

 pound, with two stipulae. 



Chiefly found in temperate or cold 

 northerly climates ; very few within the 

 tropics ; fourteen British genera. The 

 whole order is innocent. Prof. Lindley. 



ROSA'CEOUS. Belonging to the order Ro- 

 sacese. Applied to polypetalous corollas, 

 consisting of four or more petals, spread- 

 ing like a rose. 



ROMA'NZOVITE. A mineral recently dis- 

 covered in Finland. It is of a brown, 

 brownish yellow, and blackish- brown co- 

 lour. It has been named after Count 

 Romaiizoff. According to the analysis 

 of M. Julin, it consists of silica 41 '22. 

 lime 24-78, alumine 24-08, oxide of 

 iron 7-02, magnesia and oxide of man- 

 ganese 0-92. 



RO'SIN. See Resin. 



ROSTELLA'RIA. A genus of marine uni- 

 valves, found both recent and fossil. A 

 slightly turreted or fusiform univalve, 

 terminating at its base in a lengthened 

 canal, similar to a sharp beak. The lip 

 whole or dentated, and dilated with 

 age ; with a groove contiguous to the 

 canal. 



The most remarkable fossil shell of this 

 genus is Rostellaria macroptera, found 

 in Hampshire, and in France. This large 

 and handsome fossil is remarkable for 

 the size of its right lip, which is formed 

 into a wide, round, and rather thin wing, 

 extending from the canal at the base, 



