SALT. 
437 
of more than six hundred feet ; in Spain we find 
it both on a level with the plains, and several hun- 
dred feet above ; in Tirol it is still more elevated, 
and in Peru it is found on the summit of the Andes, 
more than two thousand fathoms above the surface 
of the sea. 
The only mines of rock salt in England are those 
near North wich, in the county of Chester, disco- 
vered, about a mile from the town, in the year 
1670 . The beds of salt in these mines are found 
from 80 to 140 feet below the surface of the earth. 
They vary in thickness, and lie in an undulating 
or waved direction. We learn from some observa- 
tions made upon the spot, that the first stratum, or 
mine, is from fifteen to twenty-one yards in thick-* 
ness, in appearance resembling brown sugar candy, 
perfectly solid, and so hard as to be broken with 
great difficulty by iron picks and wedges. This 
part of the business, however, has lately been much 
accelerated by gunpowder, with which the work- 
men loosen and remove many tons together. Be- 
neath this stratum is a bed of hard stone *, con- 
sisting of large veins of flag, intermingled with 
some rock salt, the whole from twenty-five to thirty- 
five yards in thickness. Under this bed is a second 
stratum, or mine of salt, from five to six yards thick; 
many parts of it perfectly white, and clear as crystal ; 
others brown ; but all less impure than the upper 
* This must be considered as a very singular occurrence, and 
perhaps the only instance where a stratum of hard stone has been 
found between layers of salt. 
