222 
MUR! A. 
heated, of a cubic form, difiolved in water. Of this there 
are three varieties, as it occurs, i. in the ocean ; z. in fait 
lakes ; 3. in fait fprings. When evaporated, it generally 
contains from zo to 30 per cent, of muriat of foda. 
z. Muria montana, common or rock fait, or muriat of 
foda : fixed, decrepitating in the fire, dry, pure, producing 
fulphat of foda when faturated with fulphuric acid. 
Found in Britain, Poland, Hungary, Spain, and various 
other countries, fometimes forming vaft mafles and moun¬ 
tains. It is found colourlefs, and of various fhades of 
grey, yellow, red, blue, or brown. It is frequently con¬ 
taminated by a mixture of muriat of lime, muriat of mag- 
nefia, or other earths ; and may be purified by dropping 
into it firft a folution of carbonat of barytes, then of car- 
bonat of foda, as long as any precipitate continues to fall; 
then fe pa rate the precipitate by filtration, and evaporate 
flowly till the fait cryftallizes : it is foluble in fomething 
lefs than three times its weight of water. Specific gra¬ 
vity 2.-12. Contains acid 52, foda.42, water of cryftal- 
lization 6. 
Rock-falt is generally accompanied by gypfum and in¬ 
durated ochry clay ; and is always fituated among fecon- 
dary ftrata. In l'ome parts of the world it has been em¬ 
ployed inftead of Hone, in building: this ufe of it is men¬ 
tioned by Strabo and Pliny. The rock-falt of Chefhire is 
of a brownifh red colour, in confequence of the prefence 
of an ochry clay : this clay is immediately feparated by 
folution and cryftallization ; fubfiding to the bottom of 
the water in which the fait has been dilfolved, and leaving 
the fupernatant liquor clear; from which the fait may be 
recovered by evaporation of the water that held it in fo¬ 
lution, in a perfedily colourlefs ftate. Tranfparent co¬ 
lourlefs patches of fait occur here and there in the natural 
ftratum; but, upon the whole, this is of the colour above 
del’cribed, and the appearance of the mine is much the 
fame as of a quarry of common fbone of the fame colour. 
Mr. Playfair deferibes a peculiarity in the rock-falt of 
Chefhire : he fays that the mafs is compadf, but arranged 
in nodules of five or fix feet in diameter ; thel'e nodules 
are not perfectly fpherical, but each is comprefled by thofe 
that furround it, fo as to have the fliape of an irregular 
polyhedron. 
The falt-mines of Chefhire are found near the centre 
of a large plain formed by the fouthern parts of Lanca- 
fliire, the northern extremity of Shroplhire, and the in¬ 
tervening county of Chefhire. This plain is fubdivided 
into three; the bafon of the Dee on the weft, of the 
Merfey on the north, and the Weaver in the middle. In 
this middle diftriif, which may be compared to a l’edtor of 
a circle, having its centre at the point where the Weaver 
falls into the Merfey (the circumference ftretching along 
the borders of Flintlhire, Shropfhire, and Staffordfliire), 
are found the falt-mines, generally not far from the banks 
of the Weaver and its branches. The falt-rock was firft 
difeovered at Marbury, near Northwdch, about a hundred 
and forty years ago, in fearching for coal. After this 
bed of rock had been worked for more than a century, a 
i'econd and inferior ftratum was met with, feparated by a 
bed of indurated clay from the one previoully known. 
This lower ftratum was afeertained to polfefs, at a certain 
depth, a great degree of purity and freedom from earthy 
admixture ; on which account, and from the local advan¬ 
tages of Northwich for exportation, the foil'd fait is now 
worked only in the vicinity of this place. The thicknefs 
of the upper bed of fait varies from twenty to thirty yards; 
that of the lower bed has never yet been afeertained. It 
is a certain faff, that no marine exuvia; or organic remains 
are found in the ftrata lituated over the rock-lalt of Che- 
Ihire. The occurrence of gypfum in connexion with beds 
of foffil fait, is a faff generally obferved ; and it occurs in 
Chefhire, as well as in the ialt-rocks on the continent. 
One of the-moft ftriking faffs connected with the internal 
itruffure of the Northwich rock-lalt, is the appearance ob- 
fervable in the horizontal feffions of the rock, of various 
ires, more or lefs diftinffly marked, and differing con- 
fiderably in the forms which they aflume; 'fome appearing 
nearly circular, others'perfectly pentagonal, and others 
again having an irregular polyhedral form. The lines 
which form the boundaries of thefe figures are compofed 
of extremely-pure fine fait, forming a divijion between 
the coarfe red rock exterior to the figure, and the equally- 
coarfe rock included within its area. TranJ'. of the Geologic 
Society, vol. i. 1811. 
The brine-fprings met with near Droitwich in Wor- 
cefterlhire, from which a great quantity of fait is feparated 
by the procefs of evaporation, probably communicate with 
ftrata of rock-falt; and perhaps thel'e ftrata may hereafter 
be difeovered; for within the laft two or three years a 
vein of gypfum has been met with in that part of Wor- 
cefterfhire, which alone might lead, to the expedition of 
finding rock-falt. 
The following account of the falt-mines in Upper Po¬ 
land, is extra&ed from Malte-Brun’s Picture of Poland.— 
There are two diftrids in Upper Poland w-orthy of claim¬ 
ing the attention of the naturalift and geographer; the 
one is that of the mines between the Pilicaand the Viftula, 
the other that of the falt-mines between the Viftula and 
the Carpathian mountains. The whoie extent of the 
chain of the Carpathian from the north, rifes into a gra¬ 
dual afeent, intermixed with fmall hills compofed of white 
clay, and fometimes of chalky piafter. Underneath this 
ftratum is found another, which confifts of a fine foft pli¬ 
able fand ; next to this land is a layer of fandy marl; and 
under this, and often in the middle of it, is f mnd the 
foffil fait. From Cracow to Lemberg, this bed of fand is 
vilible in the plain. On afeending to the height of 15a 
to 200 feet above the Viftula, the argillaceous hillocks 
commence; amongft which, wherever they make holes of 
any depth, foffil Fait and lalt-water is met with: fprings 
of fulphur and bitumen are common: in this trad of land 
are fituated the two famous falt-mines of Bochnia and 
Wieliczka. 
According to the Polifh hiftorians and geographers, 
the falt-mines of Bochnia were difeovered in 1251. This 
difeovery is attributed to St. Cunigonda, an Hungarian 
princefs, the wife of the duke Boleflas V. but attended with 
many fabulous circumftances; notwithftanding which, it 
is eafy to conclude, that fhe brought along with her fome 
Hungarian miners. They were not regularly worked, or 
well known, till 1442 ; but at prefent the falt-mines of 
Bochnia are far inferior to thofe of Wieliczka. The pro¬ 
duce of both, under the Polifh government, amounted to 
about ten millions of florins (Polifh), and the expenfes of 
working, See. to about nine-tenths of that fum. After 
the reftridions were taken off', and the encouragement 
given by the Auftrian government, it is ftated that the 
produce of the mines amounted to two millions of florins 
of Vienna, clear of all deductions. The mine of Boch¬ 
nia, according to Schober, confifted of a long fubterrane- 
ous fort of gallery or paflage, about 750 feet wide from 
north to fouth; about 10,000 feet long, in a line from eaft 
to weft ; and its depth from 100 to 1200 feet. The mine 
firft appears in cryftal f'pars, and the fait is found every¬ 
where in veins. It is rather finer than that of Wieliczka, 
efpecially where they quarry deeper. It is cut into mo- 
derate-fized pieces, in order to be put into barrels. 
Pieces of broken black wood are often found amongft the 
fait. Within the whole extent of the mine there is fo lit¬ 
tle moifture, that dull abounds in great quantities. Ala- 
bafter too is found in the mine. 
The falt-mines of Wieliczka are divided into three 
parts : that of St. John, the Old, and New Field. The 
town of Wieliczka is not only undermined, but the mines 
extend on each fide to a diftance equal to its fize; that is, 
from eaft to weft fix thoufand feet; from fouth to north, 
about two thoufand ; and in the deepeft part of the valley 
about eight hundred, according to Bufching. There are 
ten pits or lhafts ; but that knowm by the name of Wotlua- 
Gora ferves as a canal to carry oft’ the waters which filter 
through the different ftrata above ;■ for throughout the 
whole 
