18 
The first, or top rock salt, was discovered in 1670, and 
very shortly after this mines were worked, hut not to any 
large extent. It was not until 1721, when the river Weaver 
was made navigable, that the rock salt could be largely 
utilised. In the year 1732 there were sent down the Weaver 
9,322 tons of rock salt. The quantity shipped down the 
river increased year by year until in 1778 it reached 54,000 
tons. In 1781 the bottom, or lower rock salt, was discovered, 
and all new mines were sunk to it, the quality being better. 
After the commencement of the present century the top 
mines ceased to be worked, and now only one is known to 
exist. Nearly the whole of these top mines were destroyed 
by the breaking in of water or brine at the shafts. One 
after another they collapsed, leaving large funnel-shaped 
pits filled with water, locally known as “rock pit holes,” to 
mark their position. In all the upper mines large pillars, 
about 5 yards square, were left to support the roof. In the 
lower mines these pillars, though originally of the same 
size, are now left larger, varying from 8 to 1 2 yards square. 
One or two lower mines have collapsed by the roof falling 
in for want of sufficient supports. Some have been aban- 
doned because of the breaking in of brine or water. Of 
late years, however, when worked to the boundary of the 
owner, they have been allowed to fill with brine, which is 
pumped out for the manufacture of white salt. About 
150,000 tons per year of rock salt are mined from the lower 
portion of the salt bed, which is the purest. This is not 
quite one tenth of the quantity of white salt made from brine. 
Whether, however, the salt is mined as rock salt or is manu- 
factured from brine, the beds of rock salt before described 
furnish the whole. 
The manufacture of salt from natural brine is carried on 
more largely in Cheshire than in any other portion of the 
world. The brine is found upon or near to the surface of the 
first bed of rock salt. It is reached by the sinking of a shaft or 
