9,292,800 × 35 × 32 / 20 = 520,396,800 tons, or, in both beds together, 892,108,800 tons. The Winsford district, taking the beds of rock-salt at an average thickness of 65 yds., which is 5 yds. less than the figure given by Dickinson, we have 1,932,902,400 tons. As the whole of the white salt has been manufactured from brine derived from the rock-salt, it represents so many tons of rock-salt pumped up. Now, as the specific gravity of rock-salt is 2·125, a cubic yard contains 32 cwts. This being the case, we find the cubic yards of rock-salt pumped up annually in each district to be, viz.-- In WINSFORD DISTRICT-- 687,000 × 20 / 32 = 429,375 cubic yds. In NORTHWICH DISTRICT-- 587,000 × 20 / 32 = 366,875 cubic yds. In MIDDLEWICH DISTRICT-- 14,000 × 20 / 32 = 8,750 cubic yds. In SANDBACH DISTRICT-- 78,000 × 20 / 32 = 48,750 cubic yds. Making a total of 853,750 cubic yds. This represents 176·5 acres of 1 yd. thick. This is entirely independent of the rock-salt, which, at a low estimate, equals 120,000 tons per annum, or, say, 75,000 cubic yds., or 15·5 acres of 1 yd. thick. In these calculations no allowance has been made for wastage, and this is very large. During the year every pan requires picking from six to twelve times, the stoved oftener than the common. This necessitates the pan being swept out and an enormous quantity of brine wasted. Besides this, the pan scale contains a large percentage of salt. Again, in _drawing_ the salt out of the pans a large quantity of brine is wasted. Add to this also the leakage in pipes, overflow of cisterns, leakage through defective pans, etc., and the total of wastage will be very large. It is scarcely possible to estimate this, but if we calculate 10 per cent. we shall be under the mark. Thus, for waste, we may set down 136,600 tons. This would represent 85,075 cubic yds., or 17·65 acres 1 yd. thick. We thus see that 209·65 acres of rock-salt 1 yd. thick is every year consumed in the Cheshire salt district. CHAPTER VI THE CHESHIRE SUBSIDENCES