COMMON SALT. 131 
this substance ; the upper one is about forty-two yards 
below the surface, and twenty-six yards thick. This 
was originally discovered about a century and a half ago, 
in searching for coal. The lower bed has already been 
examined to the depth of forty yards, without coming 
to the bottom ; and it is about the centre of this bed 
that the purest salt has been discovered. The average 
depth of the cavity, formed by the workmen along the 
vein of salt in the different mines, is supposed to be 
about sixteen feet. In some of the mines, where pil- 
lars six or eight yards square are left to support the 
roof, the appearance of the cavity is singularly beauti- 
ful : and the effect is greatly increased when the mine 
is illuminated by numerous candles fixed to the side of 
the rock. The scene so formed would almost seem to 
realize the notion of the magic palaces of Eastern poets. 
Some of the mines are worked in aisles or streets. The 
methods employed in working out the salt offer nothing 
worthy of notice. Larger masses are separated from the 
body of the rock, by blasting with gunpowder ; and 
are afterwards broken down with pickaxes, hammers, and 
other instruments. The present number of mines in the 
vicinity of Northwich is eleven or twelve, from which 
there are raised, on an average, 50,000 or 60,000 tons 
of salt per annum. The greater part of this quantity is 
exported to Ireland and the Baltic ; and the remainder 
is employed in Cheshire, and the adjacent counties. 
Salt is also made from brine springs in Cheshire, 
Cumberland, Staffordshire, and Worcestershire ; but 
the kind most commonly used in England is that which 
is made from sea water, and has the name of sea salt. 
The mode of manufacturing it is very simple. The 
water is first pumped into shallow reservoirs of earth, 
called salt pans, or salterns. In these it remains ex- 
posed to the sun until a certain proportion of the water 
is evaporated, so as to leave it about seven times stronger 
than in its original state. It is then conducted by an- 
other pump into flat iron pans, eight or nine feet square, 
and as many inches deep. These, being placed over a 
