438 
SALT. 
stratum. The whole mass of salt is covered by a 
bed of whitish clay, used in the manufactory of 
Liverpool ware. 
The same observer informs us that rock salt-pits 
are sunk at a great expense, and are very uncertain 
in their duration ; being frequently destroyed by 
the brine springs bursting into them, and dissolving 
the pillars that support the roof; through which the 
whole work falls in, leaving vast chasms in the sur- 
face of the earth. In forming a pit, a shaft or eye 
is sunk, similar to that of a coal-pit, but more ex- 
tensive. When the workmen have penetrated to 
the salt rock, and made a proper cavity, they leave 
a sufficient substance of the rock (generally about 
seven yards in thickness) to form a solid roof ; and 
as they proceed they hew pillars out of the rock to 
sustain the roof, and then employ gunpowder to 
separate what they intend to raise. This is con- 
veyed to the surface in large craggy lumps, drawn 
up in capacious baskets made for the purpose. The 
largest rock salt-pit now worked is in the township 
of Wilton, near Northwich. This has been ex- 
cavated in a circular form 108 yards in diameter; 
its roof is supported by twenty-five pillars, each 
three yards wide at the front, four at the back, and 
its sides extending six yards. Each pillar contains 
294 solid yards of rock salt ; and the whole area of 
the pit, which is fourteen yards hollow, includes 
9160 superficial yards, being little less than two 
acres of land. We may easily conceive that when 
this wonderful place is well lighted up, the re- 
