303 
MINES, METALS, AND RKMS. 
different degrees of purity, and more or less ofe'1 ^ 
earthy and metallic substances, 
lower lied yields a rock-salt. 
,uie ur icas £S .11 
The purer port' 
which, being 
exported to the Baltic, obtains tlie name of Prns* fsf" j 
The extent of die cavity formed by the working’ jjjT 
■different mines, the average depth being 
feet. In some of the pits, where pillars from iti't 
twenty-four feet square form the supports of V 
the appearance of the cavity is singularly striking; ‘ [it 
brilliancy of the effect is greatly increased wh2** \ 
is illuminated by candles fixed to the side of the 
scene thus formed almost appears to realize ui 
palaces of the eastern poets. Some of the pits 
in aisles or streets, but the choice here is wlioUf 
‘■(ri 
Among the methods employed in working out 
-.-ti. a-U^ -C • X.. A ePpi** , 
salt, the opemtion of blasting is applied to the !(* 
large masses from tiie body of tlis rock, aed 
afterwards broken down by the meclianical 
-IICIVYOIUO Uiuiceu uuwu uy me meeiwni';-;- • 
in common use. The present number ot mines 
twelve, from which there are raised, on an annutt* (S 
fifty or sixty thousand tons of rock-salt. The 
h^AnCf .4 
of this quantity is exported to Ireland and th® f ^ in ^ 
remainder being employed in the Cheshire distr‘ ’ (f 
manufacture of white salt by solution and subseff 
poration, ^ 
The general situation occupied by the r*’' 
Cheshire is very similar to that of the Traiis)' 
ick 
iaf'iif 
Polish mines, the beds of this mineral being "f.’lifV 
small plains, bounded by hills of inconsidem^j^ (lit'l.i 
forming a kind of basin or hollow, from "‘'’If'* 
usually only a narrow egress for the waters. t 
of the Austrian salt mines near Saltzburg 
to b® .nii> . 
very different. The mineral there appears to u 
in beds of great thickness, which occur neat _ 
of limestone hills, at a great elevation above m 
country, 
allowed that rock-salt is formed from the 
sea, it is necessary to suppose the occurrence f 
of the most vast and surprising changes ! 
This is a singular fact ; and if the 0 
at rock-salt is fermed from the ^ fb'lt 
The theory of tiie formation of rock-salt 
difficulties, at the same time that little doubt c 
the general foct, tliat the beds of this naiuctiu 
