It o c 



powder, or dugout of it in other ways, as is frequently the 

 cafe in forming and laying out ornamented grounds. 



But partial concealment may often take place in circum- 

 stances of this kind, and is, it is fuppofed, bell effected by 

 wood ; and in cafe the form of the part or parts, which ap- 

 pear, be in the grand ftyie, and the concealment accom- 

 plished in a judicious manner, the imagination, winch is 

 ready to magnify the extent or power of indiftintt objects, 

 will, it is fuppofed, conceive the reft to be much more 

 noble, thnn it they had been of forms capable of being ad- 

 vantageoufly difclofed. Partial concealment may likewife 

 iometimes be effedted by earth or water, and even by build- 

 . ; in all of which, the general principles are the fame, 

 it is fuppofed. 



It is ftatcd, that is rendering rocks more charafteriftic, 

 iirlt requisite is to attend to their general characters : 

 thele may either be grand, terrific, fanciful, or romantic 

 and pici'irefque. Grandeur here conlills, it is fuppofed, 

 commonly in the breadtli of light and fliade, or the height 

 of the maffes ; and may be heightened by increafing thefe, 

 either by removing fmail parts of the rock itlelf, or by 

 clearing away the appertaining matters, which tend to con- 

 ceal or injure the principal maffes. Romantic or terrific- 

 rocks may, it is thought, fometimes be improved by con- 

 cealment or djfclofure, but rarely by increafing their cha- 

 racter, And thole of pifturefque beauty may often be 

 operated upon with fuccefs, either by giving more breadth, 

 variety, or intricacy to the rocks themfelves ; or by covering 

 with vegetation ; or planting trees before them, to 

 ellect variety or harmony ; or bulhes and creepers above 

 i, to harlg over and produce (hade and intricacy. An 

 excels of intricacy is, however, fuggefted, as dangerous, 

 and as tending more than any other quality to make a rock 

 trilling. Crags are faid to be frequently trifling on this ac- 

 count, as well as the rock in different lituations. In Ihort, 

 the management of rocks, it is imagined, is yet very little, 

 it at all, underftood in this country. In many parts they 

 are indeed ieen (hewn, but in fuch a way as that they ap- 

 pear little better than upright maffes of red earth. The 

 Subject: is unqueltionably deferving of more attention than it 

 has hitherto met with, from the deiigners of ornamented 

 grounds. 



Rock- 11^0)1, any fort of work or defign, which is formed 

 of the parts or fragments of rocks, or large ltone6, in gar- 

 dens or pleafure-grounds. 



All works of this nature fhould be contrived in fuch a 

 manner, as to harmonize as much as poflible with the pe- 

 culiarities of the lituations or places in which they are made. 

 See Rock and Stone. 



They were formerly much more common, in botli thefe 

 fituations, than they are at prefent. 

 Rock Alum. See Ai.r.M. 



RocK-Butter, in Mineralogy, a (aline mineral, formed in 

 the fifiures of rocks of alum-llate. It occurs both maffive 

 and UaLicHtical, and fometimes pulverulent. It has a 

 greyifh-whitc or a draw-yellow colour, and a fweetifh and 

 fomewhat acidulous allringcnt tailc, like alum. Ii i in 

 deed a k:;id of native alum. The feel is fomewhat greafy, 

 from which and its colour it has received i 



RoCK-Cori, Suber Montanum, a flexible and Son 

 elallic mineral, found in mineral veins. It is ■■ 

 mafiive, and fometimes in laminse or plate:, : thele have I 

 called rock-leather and ruck-flelh. The common colour is 

 a yellowiSh-grey of various (hades: it is fometimes a ycl- 

 lowifh-brown and cream-colour. It has a fibrous flruc- 

 tur and but little lullre. The fractured furface is deli- 

 cately uneven. This mineral is opaque, and very loft, 

 Vol. XXX. 



R O C 



yielding to the nail. 



It breaks with great difficulty, 



and cracks when handled : it is fo light as to fwim on 

 water, aud is almolt infufible in the flame of the blow 

 pipe. 



The constituent parts, as given by Bergmann, ai 

 Silex - 



Magnefia 



Alumine ... 

 Lime 

 Iron ... 



Rock-cork approaches in its nature to afbeftus, from 

 which it differs principally by the promifcuous arrangement 

 of the fibres. 



Ro( K-Cnjlah the pureft variety of cryftallized quartz. 

 (See Quartz.) This (lone is fometimes employed in 

 jewellery, and is differently named, according to the places 

 from whence it is procured, as Briltol ftone, Scotch 

 pebbles, &c. 



RoCK-Fifi, a common Englifh. name for the gobius ma- 

 rums, or lea-gudgeon. See Gonius Niger. 



Rock Germander, in Botany, a fpecies of veronica: 

 which fee. 



Rock-O//. See Petroleum. 



RocK-Ouzel, in Ornithology. See Ring Ouzel, and 

 Amzel. 



RoCK-Rofe, in Botany. See ClSTUS. 



ROCK-Sak, in Mineralogy and Geology, a natural fait, of 

 the fame kind as common table fait. This uletul mineral 

 forms large beds and maffes in many parts of the world, and 

 even compofes entire mountains. It occurs in large colum- 

 fpheroidal concretions, and alfo cryftallized in 



nar or 



cubes. Rock-falt is fubdivided by Werner into two kinds, 

 foliated and fibrous. The more common colours of foliated 

 rock-falt are, white, grey, reddilh-brown, and red; but 

 fometimes it is violet, (ley-blue, and green, and is more 

 or lefs tranfparent or pellucid : it breaks into cubical frag- 

 ments, which have a vitreous luftre : the llruc"ture is indif- 

 tinftly foliated. In fibrous rock-falt the fibres are generally 

 fmall and curved ; in other refpefts it differs little from the 

 former. The tafte of both is like that of common fait. 

 The red varieties are coloured by earthy matter and oxyd of 

 iron ; the white and tranfparent are extremely pure, being 

 compofed almoft entirely of muriatic acid and foda, or, ac- 

 cording to Davy, of chlorine and (odium. In the pureft kind 

 alfo, there is fcarcely any trace of water of cryltallization. 

 According to Henry, pure tranfparent rock-falt, calcined 

 for half an hour in a low red heat, equal to four or five de- 

 grees of Wedgewood's pyrometer, loft abfolutely nothing of 

 its weight. It is remarkable, alfo, that if free from any 

 adventitious moifture, it may be Suddenly and ftrongly 

 heated with fcarcely any of that found called decrepitation, 

 which i> produced by a limilar treatment of all thi 

 of in ' ' ed common fait. The fpecific gravi 

 pun ,1 Specimens of rock-falt is about 2.170, o? the left pure 



about 2. J 30. * 



Rock-falt ii widely dillributed over the globe ; it app 

 ipally in the lower fecondary Hrata. It is molt' 

 quently accompanied with fulphate of lime or gypfum, and 

 by bed . ..I clay impn gnated with fait. Belide the fed- 01 

 rock-falt which are known, numerous brine-fprings in va- 

 rious part-; of the world atteft the exillence of tin's mineral 



deep 1 Surface, as it i. evident thefe Springs perco- 



I fait, or Strata impregnated with it. Several brine- 



, have recentl) been difcovercdin the deep coal-mine* 



3 E 01 



