On Subsidences in the Salt Districts of Cheshire. 135 



Wilton is about 450 yards in circumference, and there are many 

 of 250 yards near North wich.* 



The subsidences due to the latter cause are widely extended. 

 At Wilton Mill, in the valley of the Weaver, above Northwich, a 

 large mere (or lake) is now in course of formation, and has been 

 observed to widen its banks since 1790. In 1857 the water 

 covered an area of about 1,300 yards in length, and 400 in breadth, 

 and since then there have been several fresh depressions. 



The two lakes called Budworth mere and Pick mere, north of 

 Northwich, have visibly extended — and as they lie in the same 

 valley — they will doubtless ultimately coalesce. Hollows are 

 also being formed at Birches Hall near Winsford, Billinge-green, 

 between Sandbach and Northwich, and near Martin Hall. In 

 the neighbourhood of Crewe, Winsford, Middlewich and other 

 places, the ground has been undergoing a process of lowering for 

 many years, and these have culminated in the recent disastrous 

 subsidences at Northwich, which have been graphically described 

 in the public press. 



At Northwich the depth at which the brine is found is about 

 132 feet below the canal level,t and it is kept down by continuous 

 pumping nearly to that depth. This is about the depth of the 

 upper bed of rock salt. When just tapped, the brine usually 

 rushes in with force. The earlier attempts at sinking into the 

 strata containing the brine — especially amongst old workings of 

 salt-rock — were exceedingly hazardous;}: ; recently the tapping 

 of the brine is more safely effected by the aid of iron cylinders, 

 as described by Mr. Dickenson in his interesting Report. 



From what has been stated above, it will be clear that the 

 Northwich subsidences are due to the solution of the surface of 

 the upper bed of rock-salt, owing to the constant pumping of 

 brine, from which the salt of commerce is obtained. Some idea 

 of the extent to which this process is carried may be formed 

 when it is known that upwards of one million tons (of twenty-six 

 cwt.) are annually obtained by evaporation of brine in Cheshire 



* The term "-wich" is an old Saxon name for a salt spring. It is used in the "Dom 

 hoc " or Domesdaj' Book. 



f The canal is ninety-six feet above the level of an ordinary spring tide at Kuncorn 

 so if all the salt-rock were dissolved away the valley would be submerged deeply. 



J Tlie processes are described by Mr. Dickenson's Report, p. 22. 



