ROC 



[ 386 



BOD 



divided into those of aqueous and 

 igneous origin, from the two agents 

 known to us as capable of their 

 production. Bocks are also divided 

 into primary, transition, secondary, 

 tertiary, &c. 



BOCK BTJ'TTEK. Native alum. It 

 occurs in the cavities or fissures of 

 argillaceous slate in soft masses ; it 

 is of a yellowish- white colour; a 

 little unctuous to the touch ; mas- 

 sive, tuberose, or stalactical. It is 

 mingled with clay and oxide of 

 iron. 



BOCK CBT'STAL. Called also Moun- 

 tain Crystal. The Berg Crystal of 

 Werner. This, which is only the 

 most perfect variety of quartz, has, 

 when crystallized, received the 

 name of rock crystal: the same 

 name has been extended to coloured 

 crystals, when transparent. Bock 

 crystal is usually limpid, colour- 

 less, and as transparent as glass; 

 it is, however, occasionally met 

 with coloured, passing from white 

 into yellow, brown, red and brown- 

 ish black. The finest specimens 

 of rock crystal are found in Dau- 

 phine, in the Alps, in Madagascar, 

 &c. ; but it abounds in every coun- 

 try, in all parts of the world, in 

 chasms or clefts of the oldest rocks. 

 The primitive form is a rhomboid 

 of 94 15' and 85 45'; the second- 

 ary forms are an equiangular six- 

 sided prism, rather acutely acumi- 

 nated on both extremities by six 

 planes, which are set on the lateral 

 planes ; a double six-sided pyramid ; 

 an acute simple six-sided pyramid, 

 and acute double three- sided pyra- 

 mid. Splendent ; fracture perfect 

 conchoidal; gives double refraction 

 when viewed through a pyramidal 

 and lateral plane at the same time. 

 It is perfectly infusible before the 

 blow-pipe, and is sufficiently hard 

 to scratch glass. Its specific gra- 

 vity is from 2-5 to 2*8. By fric- 

 tion it exhales a peculiar odour, 

 and some varieties also phospho- 



resce in the dark. An analysis by 

 Bergman gave silex 93, alumine 6, 

 lime 1 . Bucholz states it to con- 

 sist of silica 99|, with a trace of 

 ferruginous alumina. 



BOCK WOOD. A variety of asbestus 

 of a brown colour ; in its general 

 appearance greatly resembling fos- 

 sil wood. 



BOCK CORK. 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, iron 31. It occurs in Prance, 

 Germany and some other countries. 



BOCK SALT. Common salt. This is 

 found in vast solid masses or beds, 

 in different formations, but most 

 extensively in the new red sand- 

 stone formation. Although rock 

 salt, salt mines, and salt springs 

 are most frequently found to occur 

 in the new red sandstone formation, 

 (from which circumstance many 

 geologists have applied to it the 

 name of saliferous formation) yet 

 are they not confined to them. 

 The salt mines of Wieliezka and 

 Sicily are in tertiary formation ; 

 those of Cardona are in the chalk 

 series ; some are in the oolitic de- 

 posits ; and in the county of 

 Durham salt springs occur in the 

 carboniferous series. 



The saliferous strata of North- 

 wich, form two beds of great 

 thickness, 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 explained. 



BODE'NT. An animal belonging to 

 the order Bodentia, or gnawers. 



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

 The fifth order of Mammalia : call- 

 ed also Gnawers. The order contains 

 many genera, some of which are 

 familiar to us, namely, the squirrel, 



