Orvetogno. discovered a plain on the summit of the chain of lime- 

 y. stone mountains that bound the desart of Lybia to the 

 ''""V""' north, consisting of a mass of rock-salt, spread over so 

 large a tract of surface, that in one direction no eye 

 could reach its termination, and its width he computed 

 at several miles. To the south-east of Abyssinia, there 

 is a plain of rock-salt four days journey across, whence 

 all that country is supplied +. At Tegazza, and in seve- 

 ral other places in Sahara, very large beds of pure rock- 

 talt occur under strata of different kinds of solid rock ; 

 and beds of salt appear at Darfur, and in the country of 

 Congo. 



Atia. There is a considerable mine of rock-salt 

 twenty versts from Jena-Tayerska, in the desart be- 

 tween the Volga and the Uralian Mountains ; another 

 named Iletzki, near Astracan ; and there are several 

 others in Siberia $. Salt mines are worked in that part 

 of China which borders on Tartary. At Teflis, Tauris, 

 and other places in Persia, there are great masses of 

 rock-salt ; and we are informed, that in the desart of 

 Caramania, and also in Arabia, rock-salt is so abun- 

 dant, and the atmosphere is so dry, that the inhabitants 

 use it for building house*. The Island of Ormuz, si- 

 tuated in the mouth of the Persian Gulf, is principally 

 composed of rock-salt. Rock-salt is one of the mineral 

 productions of the valley of Cashmere ; and in the pro- 

 vince of Lahore in India, there is a hill of rock-salt 

 equal to that of Cordona ; the salt of this bill is cut into 

 dishes, plates, and stands for lamp*. 



America. Rock-salt is found in vast quantity on the 

 elevated desart* of Peru, where it is very hard, and ha.s 

 usually a violet colour ; also in the Cordilleras of New 

 Granada, at the height of 2000 toises. It occurs in 

 considerable quantity in Upper Louisiana ; and great 

 masses of it have been found at the junction of the 

 stream of Atha-pus-caou with the Atlia-pus-caou lake ; 

 and in California. 



Nen Holland. According to Governor Hunter, it 

 i* found in considerable quantity on the east coast of 

 New Holland. 



L'ta.lt uses are very various and important. We 

 i use of it daily as a seasoning for our food : vast 

 titic* are employed for the preservation of animal 

 , butter, Ac. ; it is also used in the manufacture of 

 earthen ware, soap-making, and in many metallurgic 

 operations. It affords muriatic acid and soda by certain 

 ftfipfr*! processes. It is sometimes employed in its 

 crude sUte, but is more commonly purified. 



SECOND SUBSPECIES. 



LAKE-SALT, Jameton. Sresali, Werner. 



Eriemal Character*. Colour greyish-white. Oc- 

 curs in coarse and small roundish grains. Internal- 

 ly shining or glistening, and the lustre resinous. 

 Fracture is imperfect foliated. In other characters it 

 agrees with the other subspecies. 



OeogiKHtic and Geographic Situations. It is found 

 on the bottoms and sides of salt-lakes. In Europe, 

 Asia, and alto in Africa and America. 



CLASS II. 

 Tasteless. Specific gravity above 1 .8. 



MINERALOGY. 



OBDER I. HALOIDE. 



479 



Oryctogno. 



No metallic kistre. Streuk not changed in the order I. 

 colour. Haloide. 



Cleavage. If in the direction of a four-sided prism, 

 the hardness is equal to 4 and less : if axifrangible and 

 prismatoidal, the hardness and specific gravity are be- 

 low 3. Hardness ranges from 1.5 to 5. If the hard- 

 ness is less than '2.5, the specific gravity will be 2.4. 

 and less. Specific gravity ranges from 2.2 to 3.2. 

 If less than 2.4, the hardness will be 2.4, and less. 



GENUS I. GYPSUM. 



Three axes. Cleavage prismatic. Hardness =1.5 GTMOH. 

 3.5. Sp. gr. =2.2 3.0. 



1. AXIFHANGIBLE GYPSUM, Jometon. Axentheilen- Axifrangi. 

 des Gyps-Hloide, Moht. biegyp- 



Pristn =113 8'. Cleavage perpendicular to the *" m - 

 axis, or axifrangible. Hardness = 1.5 2.0. Sp. gr. 

 =2.22.4. 



Thi* species contain! six subspecies, viz. Spirry 

 Gypsum or Selenite, Foliated Granular Gypsum, Com. 

 pact Gyptum, Fibrous Gypsum, Scaly Foliated Gyp- 

 sum, and Earthy Gypsum. * Montmartrite. 



FIRST SUBSPECIES. 

 SPARRY G VPSUM OR SELENITE, Jamcton. Fraueneis, 



tr fTHtr. 



External Characlert. Colours smoke-grey, greyish- Stlenite. 

 white, snow-white, greenish-white, and yellowi.-h- 

 white, and also wax-yellow, pale ochre-yellow, and 

 yellowish-brown. Sometimes dark-brown, owing to 

 intermixed stinkstone. Some varieties display irides- 

 cent colours. Occurs massive, coarsely disseminated, 

 also in distinct concretions, which are large and coarse 

 granular, and sometimes inclining to thick lamellar; 

 and crystallized. The following are some of the se- 

 condary figures : 



1. Six-sided prism. 2. Lens. 3. Twin-crystals. 

 These are either formed by two lenses, which are at- 

 tached by their faces, or by two six-sided prisms pushed 

 into each other in the direction of their breadth, in 

 such a manner, that the united summits at one extre- 

 mity form a re-entering angle, but at the other a salient 

 angle, or four-planed acumination. When two such 

 twin crystals are pushed into each other in the direction 

 of their length, a 4. Quadruple crystal is formed. 



Lateral planet of the prism sometimes smooth, some- 

 times longitudinally streaked, and shining ; the convex 

 terminal faces, and lens, are rough and dull. Internally, 

 lustre splendent and pearly. Cleavage threefold ; the 

 most distinct cleavage perpendicular to the axis of the 

 prism ; the other two parallel with the lateral planes of 

 the primitive prism. Cleavages generally straight, and 

 sometimes curved. Fragments rhnmboidal, in which 

 two of the sides are smooth and splendent, and four are 

 streaked and shining. Alternates from semi-transpa- 

 rent to transparent, and in the latter case is observed 

 to refract double. Sectile. Very easily frangible. In 

 thin pieces flexible, but not elastic. 



Chemical CAarocffr*. Exfoliates before the blow- 

 pipe, and, if the flame is directed towards the edge of 



t Bruce rnemionj, tht in mat 

 rpnkt of rock-Mlt in the 



para of Abjwni*. cubic piece* of rock-nlt pui SI current coin. 



ic nctghbouihood of the liter Jaik, which it wmetimci to hard u to tfiap the pick-axet nude Me of la 



