Taking the fits as proved, we will now look more closely beneath the pie-crust of Northwich. The best way to do so is to get into a big tub which will just hold two people and go down the shaft of a salt mine, lowered by a windlass. First of all you pass through 32 feet of soil and drift, and then about 92 feet of what would commonly be called rock. Then below these 124 feet you come to the first bed of rock salt, which averages about 75 feet in thickness. Passing through this you come to 30 feet more of rock, and below again is found another bed of rock salt, which averages in thickness about 90 feet. It is the lower bed of rock salt which is mined. The bottom of the mine down which I went was 330 feet below the surface, but the atmosphere was delightful, being cool and dry and not in the least oppressive. A magnificent chamber, 25 feet high and 17 acres in extent, had been dug out of the salt, and its extent could easily be gauged by the help of the candles which had been lit all round the mine. Massive pillars of salt of 10 or 12 feet square are left at intervals of 25 yards to support the roof. The rock is got largely by blasting. A hole is drilled, and into the bottom of the hole a small powder ball is put. Loose powder is placed in a piece of straw and the straw is lighted. In a few seconds it burns down to the powder ball, and the rock salt which has lain so quietly in its bed for æons breaks up, and in process of time may find itself in any quarter of the globe. [Illustration: _T. Birtles, photo._] [_Warrington._ A FLOOD IN THE STREETS OF NORTHWICH.] No damage is done to the surface by the mining of this lower bed of rock salt. It is too deep for that. The subsidences are all connected with the upper bed of salt. These upper beds used to be worked because the lower beds were not known, and when they were neglected they fell in, and in this way the large sheets of water of which I have spoken were formed above the earth's crust. [Illustration: _T. Birtles, photo._] [_Warrington._ HOUSES WHICH COLLAPSED OWING TO A SUBSIDENCE.] But the mining of the upper bed of salt by man does not account for the subsidences here recorded. The name of the dangerous miner is "water." When water reaches the upper bed of salt it dissolves it as water does snow. Water can take in 26 degrees of salt and no more, and then it is called brine. Underneath Northwich is a sea of brine which lies on the top of the upper bed of salt rock. From this brine white salt is made by a process of evaporation, and that is why all over Northwich you see numbers of pumping stations which pump up the brine as fast almost as it is made. As the brine is taken out fresh water flows in and takes up its 26 degrees of salt. In this way the great cavities under Northwich which cause all the subsidences are made; they will grow bigger and bigger as long as the pumping up of brine is continued.